x86/asm: Don't use the confusing '.ifeq' directive

I find the '.ifeq <expression>' directive to be confusing.  Reading it
quickly seems to suggest its opposite meaning, or that it's missing an
argument.

Improve readability by replacing all of its x86 uses with
'.if <expression> == 0'.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrei Vagin <avagin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/757da028e802c7e98d23fbab8d234b1063e161cf.1508516398.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_64.S

@@ -817,7 +817,7 @@ ENTRY(\sym)
 
 	ASM_CLAC
 
-	.ifeq \has_error_code
+	.if \has_error_code == 0
 	pushq	$-1				/* ORIG_RAX: no syscall to restart */
 	.endif