tests/fate/source-check: Use git grep in place of grep

grep -L is not posix, solaris default grep does not support it
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

tests/fate/source-check.sh

@@ -27,7 +27,7 @@ for f in `git ls-files | grep '\.h$'` ; do
         -e 's/_vaf_/_/' \
     | tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ`"
 
-    grep -L "^#define $macro$" $f
+    git grep -L "^#define $macro$" $f
 done
 
 echo "Use of av_clip() where av_clip_uintp2() could be used:"