csky: cmpxchg: Coding convention for BUILD_BUG()

Use BUILD_BUG() instead of the custom bad_xchg.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>

arch/csky/include/asm/cmpxchg.h

@@ -4,10 +4,9 @@
 #define __ASM_CSKY_CMPXCHG_H
 
 #ifdef CONFIG_SMP
+#include <linux/bug.h>
 #include <asm/barrier.h>
 
-extern void __bad_xchg(void);
-
 #define __xchg_relaxed(new, ptr, size)				\
 ({								\
 	__typeof__(ptr) __ptr = (ptr);				\
@@ -46,7 +45,7 @@ extern void __bad_xchg(void);
 			:);					\
 		break;						\
 	default:						\
-		__bad_xchg();					\
+		BUILD_BUG();					\
 	}							\
 	__ret;							\
 })
@@ -76,7 +75,7 @@ extern void __bad_xchg(void);
 			:);					\
 		break;						\
 	default:						\
-		__bad_xchg();					\
+		BUILD_BUG();					\
 	}							\
 	__ret;							\
 })
@@ -107,7 +106,7 @@ extern void __bad_xchg(void);
 			:);					\
 		break;						\
 	default:						\
-		__bad_xchg();					\
+		BUILD_BUG();					\
 	}							\
 	__ret;							\
 })
@@ -139,7 +138,7 @@ extern void __bad_xchg(void);
 			:);					\
 		break;						\
 	default:						\
-		__bad_xchg();					\
+		BUILD_BUG();					\
 	}							\
 	__ret;							\
 })