[GFS2] Make file_read_actor export _GPL

Make file_read_actor export a _GPL export.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

mm/filemap.c

@@ -1044,7 +1044,7 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
 	desc->arg.buf += size;
 	return size;
 }
-EXPORT_SYMBOL(file_read_actor);
+EXPORT_SYMBOL_GPL(file_read_actor);
 
 /*
  * This is the "read()" routine for all filesystems