Cosmetic change: remove the whitespace after 'defined'

Originally committed as revision 12501 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/mem.h

@@ -48,7 +48,7 @@
     #define av_malloc_attrib
 #endif
 
-#if defined (__GNUC__) && (__GNU__ > 4 || __GNU__ == 4 && __GNU_MINOR__ > 1)
+#if defined(__GNUC__) && (__GNU__ > 4 || __GNU__ == 4 && __GNU_MINOR__ > 1)
     #define av_alloc_size(n) __attribute__((alloc_size(n)))
 #else
     #define av_alloc_size(n)