treewide: Remove uninitialized_var() usage

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.

In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:

git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
	xargs perl -pi -e \
		's/\buninitialized_var\(([^\)]+)\)/\1/g;
		 s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'

drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.

No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
alpha, and m68k.

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Reviewed-by: Leon Romanovsky <leonro@mellanox.com> # drivers/infiniband and mlx4/mlx5
Acked-by: Jason Gunthorpe <jgg@mellanox.com> # IB
Acked-by: Kalle Valo <kvalo@codeaurora.org> # wireless drivers
Reviewed-by: Chao Yu <yuchao0@huawei.com> # erofs
Signed-off-by: Kees Cook <keescook@chromium.org>

arch/mips/mm/init.c

@@ -83,7 +83,7 @@ void setup_zero_pages(void)
 static void *__kmap_pgprot(struct page *page, unsigned long addr, pgprot_t prot)
 {
 	enum fixed_addresses idx;
-	unsigned int uninitialized_var(old_mmid);
+	unsigned int old_mmid;
 	unsigned long vaddr, flags, entrylo;
 	unsigned long old_ctx;
 	pte_t pte;

arch/mips/mm/tlb-r4k.c

@@ -119,7 +119,7 @@ void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		if (size <= (current_cpu_data.tlbsizeftlbsets ?
 			     current_cpu_data.tlbsize / 8 :
 			     current_cpu_data.tlbsize / 2)) {
-			unsigned long old_entryhi, uninitialized_var(old_mmid);
+			unsigned long old_entryhi, old_mmid;
 			int newpid = cpu_asid(cpu, mm);
 
 			old_entryhi = read_c0_entryhi();
@@ -213,7 +213,7 @@ void local_flush_tlb_page(struct vm_area_struct *vma, unsigned long page)
 	int cpu = smp_processor_id();
 
 	if (cpu_context(cpu, vma->vm_mm) != 0) {
-		unsigned long uninitialized_var(old_mmid);
+		unsigned long old_mmid;
 		unsigned long flags, old_entryhi;
 		int idx;
 
@@ -382,7 +382,7 @@ void add_wired_entry(unsigned long entrylo0, unsigned long entrylo1,
 #ifdef CONFIG_XPA
 	panic("Broken for XPA kernels");
 #else
-	unsigned int uninitialized_var(old_mmid);
+	unsigned int old_mmid;
 	unsigned long flags;
 	unsigned long wired;
 	unsigned long old_pagemask;