[GFS2] Export file_read_actor

Export file_read_actor so that it can be used from modules since
functions which take this function as an argument are already
exported.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/mm/filemap.c b/mm/filemap.c
index 44da3d4..7624c26 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -981,6 +981,7 @@
 	desc->arg.buf += size;
 	return size;
 }
+EXPORT_SYMBOL(file_read_actor);
 
 /*
  * This is the "read()" routine for all filesystems