signal: Fix name of SIGEMT in #if defined() check

Commit cc731525 ("signal: Remove kernel interal si_code magic")
added a check for SIGMET and NSIGEMT being defined. That SIGMET should
in fact be SIGEMT, with SIGEMT being defined in
arch/{alpha,mips,sparc}/include/uapi/asm/signal.h

This was actually pointed out by BenHutchings in a lwn.net comment
here https://lwn.net/Comments/734608/

Fixes: cc731525 ("signal: Remove kernel interal si_code magic")
Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/signal.c

@@ -2698,7 +2698,7 @@ enum siginfo_layout siginfo_layout(int sig, int si_code)
 			[SIGSEGV] = { NSIGSEGV, SIL_FAULT },
 			[SIGBUS]  = { NSIGBUS,  SIL_FAULT },
 			[SIGTRAP] = { NSIGTRAP, SIL_FAULT },
-#if defined(SIGMET) && defined(NSIGEMT)
+#if defined(SIGEMT) && defined(NSIGEMT)
 			[SIGEMT]  = { NSIGEMT,  SIL_FAULT },
 #endif
 			[SIGCHLD] = { NSIGCHLD, SIL_CHLD },