fs/ceph: Move a dereference below a NULL test

If the NULL test is necessary, then the dereference should be moved below
the NULL test.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/).

// <smpl>
@@
type T;
expression E;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
  ... when != E
      when != i
  if (E == NULL) S
+ i = E->fld;
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/osd_client.c

@@ -1249,11 +1249,12 @@ int ceph_osdc_writepages(struct ceph_osd_client *osdc, struct ceph_vino vino,
 static void dispatch(struct ceph_connection *con, struct ceph_msg *msg)
 {
 	struct ceph_osd *osd = con->private;
-	struct ceph_osd_client *osdc = osd->o_osdc;
+	struct ceph_osd_client *osdc;
 	int type = le16_to_cpu(msg->hdr.type);
 
 	if (!osd)
 		return;
+	osdc = osd->o_osdc;
 
 	switch (type) {
 	case CEPH_MSG_OSD_MAP: