[S390] cio: Include linux/string.h in schid.h.

schid.h needs string.h for memset and memcmp.
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

include/asm-s390/schid.h

@@ -11,6 +11,7 @@ struct subchannel_id {
 } __attribute__ ((packed, aligned(4)));
 
 #ifdef __KERNEL__
+#include <linux/string.h>
 
 /* Helper function for sane state of pre-allocated subchannel_id. */
 static inline void