s390x: add syscall number for s390_guarded_storage from linux v4.12

new syscall in linux commit 916cda1aa1b412d7cf2991c3af7479544942d121

arch/s390x/bits/syscall.h.in

@@ -320,5 +320,6 @@
 #define __NR_copy_file_range            375
 #define __NR_preadv2                    376
 #define __NR_pwritev2                   377
+#define __NR_s390_guarded_storage       378
 #define __NR_statx                      379