Silence "string-plus-int" warning shown by clang.

libswscale/utils.c:89:42: warning: adding 'unsigned long' to a string does not append to the string [-Wstring-plus-int]

libswscale/utils.c

@@ -86,7 +86,7 @@ const char *swscale_configuration(void)
 const char *swscale_license(void)
 {
 #define LICENSE_PREFIX "libswscale license: "
-    return LICENSE_PREFIX FFMPEG_LICENSE + sizeof(LICENSE_PREFIX) - 1;
+    return &LICENSE_PREFIX FFMPEG_LICENSE[sizeof(LICENSE_PREFIX) - 1];
 }
 
 typedef struct FormatEntry {