[S390] Fix compile error in swab.h

The inline assembly in__arch_swab16p causes compile errors of the form:

*error*: *invalid* '*asm*': operand number missing after %-*letter*

The assembly uses the %O<n>/%R<n> notation but the first operand misses
the operand number, it needs to be "%O1" instead of "%O".

Reported-by: Gil Peleg <gilpeleg@servframe.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/swab.h

@@ -77,7 +77,7 @@ static inline __u16 __arch_swab16p(const __u16 *x)
 
 	asm volatile(
 #ifndef __s390x__
-		"	icm	%0,2,%O+1(%R1)\n"
+		"	icm	%0,2,%O1+1(%R1)\n"
 		"	ic	%0,%1\n"
 		: "=&d" (result) : "Q" (*x) : "cc");
 #else /* __s390x__ */