patch 8.2.3274: macro for printf format check can be simplified

Problem:    Macro for printf format check can be simplified.
Solution:   Add ATTRIBUTE_FORMAT_PRINTF(). (Dominique Pellé, issue #8635)
diff --git a/src/channel.c b/src/channel.c
index 5307792..47c742d 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -229,11 +229,7 @@
 #endif
 
     static void
-ch_error(channel_T *ch, const char *fmt, ...)
-#ifdef USE_PRINTF_FORMAT_ATTRIBUTE
-    __attribute__((format(printf, 2, 3)))
-#endif
-    ;
+ch_error(channel_T *ch, const char *fmt, ...) ATTRIBUTE_FORMAT_PRINTF(2, 3);
 
     static void
 ch_error(channel_T *ch, const char *fmt, ...)