riscv: fixup max_low_pfn with PFN_DOWN.

max_low_pfn should be pfn_size not byte_size.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Signed-off-by: Mao Han <mao_han@c-sky.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/setup.c

@@ -181,7 +181,7 @@ static void __init setup_bootmem(void)
 	BUG_ON(mem_size == 0);
 
 	set_max_mapnr(PFN_DOWN(mem_size));
-	max_low_pfn = memblock_end_of_DRAM();
+	max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
 
 #ifdef CONFIG_BLK_DEV_INITRD
 	setup_initrd();