m32r: use __stringify() macro in assembler.h

Replace #x with __stringify(x).
Also, #ifndef __STR is removed and undefine __STR macro at the beginning.

The __STR() macro is still remained, because the assembler.h might be
included from assembly codes as well as C codes.
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>

arch/m32r/include/asm/assembler.h

@@ -9,14 +9,15 @@
  * This file contains M32R architecture specific macro definitions.
  */
 
+#include <linux/stringify.h>
+
+#undef __STR
 
-#ifndef __STR
 #ifdef __ASSEMBLY__
 #define __STR(x) x
 #else
-#define __STR(x) #x
+#define __STR(x) __stringify(x)
 #endif
-#endif /* __STR */
 
 #ifdef CONFIG_SMP
 #define M32R_LOCK	__STR(lock)