Add missing parentheses around the AVERROR_PATCHWELCOME macro

definition.

Originally committed as revision 22502 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/error.h

@@ -42,6 +42,6 @@
 #define AVERROR_NOTSUPP     AVERROR(ENOSYS)  /**< Operation not supported. */
 #define AVERROR_NOENT       AVERROR(ENOENT)  /**< No such file or directory. */
 #define AVERROR_EOF         AVERROR(EPIPE)   /**< End of file. */
-#define AVERROR_PATCHWELCOME    -MKTAG('P','A','W','E') /**< Not yet implemented in FFmpeg. Patches welcome. */
+#define AVERROR_PATCHWELCOME    (-MKTAG('P','A','W','E')) /**< Not yet implemented in FFmpeg. Patches welcome. */
 
 #endif /* AVUTIL_ERROR_H */