s390/debug: add _ASM_S390_ prefix to header guard

Using DEBUG_H without a prefix is very generic and inconsistent with
other header guards in arch/s390/include/asm. In fact it collides with
the same name in the ath9k wireless driver though that depends on !S390
via disabled wireless support. Let's just use a consistent header guard
name and prevent possible future trouble.
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/debug.h

@@ -4,8 +4,8 @@
  *
  *    Copyright IBM Corp. 1999, 2020
  */
-#ifndef DEBUG_H
-#define DEBUG_H
+#ifndef _ASM_S390_DEBUG_H
+#define _ASM_S390_DEBUG_H
 
 #include <linux/string.h>
 #include <linux/spinlock.h>
@@ -487,4 +487,4 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas);
 
 #endif /* MODULE */
 
-#endif /* DEBUG_H */
+#endif /* _ASM_S390_DEBUG_H */