s390/bug: Add missing CONFIG_BUG ifdef again

Fallback to generic BUG implementation in case CONFIG_BUG is disabled.
This restores the old behaviour before 'cond_str' support was added.

It probably doesn't matter, since nobody should disable CONFIG_BUG, but at
least this is consistent to before.

Fixes: 6584ff203a ("bugs/s390: Use 'cond_str' in __EMIT_BUG()")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/bug.h

@@ -4,6 +4,8 @@
 
 #include <linux/stringify.h>
 
+#ifdef CONFIG_BUG
+
 #ifndef CONFIG_DEBUG_BUGVERBOSE
 #define _BUGVERBOSE_LOCATION(file, line)
 #else
@@ -52,6 +54,8 @@ do {								\
 
 #define HAVE_ARCH_BUG
 
+#endif /* CONFIG_BUG */
+
 #include <asm-generic/bug.h>
 
 #endif /* _ASM_S390_BUG_H */