s390/nmi: keep comments consistent

The name of bit 36 of the machine check interruption code is "guarded
storage registers validity". Add the missing "validity" part in order
to be consistent with all other comments, which include this piece of
information.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/nmi.h

@@ -72,7 +72,7 @@ union mci {
 		u64 ar :  1; /* 33 access register validity */
 		u64 da :  1; /* 34 delayed access exception */
 		u64    :  1; /* 35 */
-		u64 gs :  1; /* 36 guarded storage registers */
+		u64 gs :  1; /* 36 guarded storage registers validity */
 		u64    :  5; /* 37-41 */
 		u64 pr :  1; /* 42 tod programmable register validity */
 		u64 fc :  1; /* 43 fp control register validity */