[GFS2] Use void * instead of typedef for locking module interface

As requested by Jan Engelhardt, this removes the typedefs in the
locking module interface and replaces them with void *. Also
since we are changing the interface, I've added a few consts
as well.

Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Cc: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 87b37fe..92aa0e8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1713,8 +1713,9 @@
  * a journal from another client needs to be recovered.
  */
 
-void gfs2_glock_cb(struct gfs2_sbd *sdp, unsigned int type, void *data)
+void gfs2_glock_cb(void *cb_data, unsigned int type, void *data)
 {
+	struct gfs2_sbd *sdp = cb_data;
 
 	switch (type) {
 	case LM_CB_NEED_E: