rbd: endian bug in rbd_req_cb()

Sparse complains about this because:
drivers/block/rbd.c:996:20: warning: cast to restricted __le32
drivers/block/rbd.c:996:20: warning: cast from restricted __le16

These are set in osd_req_encode_op() and they are le16.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Alex Elder <elder@inktank.com>

drivers/block/rbd.c

@@ -977,7 +977,7 @@ static void rbd_req_cb(struct ceph_osd_request *req, struct ceph_msg *msg)
 	op = (void *)(replyhead + 1);
 	rc = le32_to_cpu(replyhead->result);
 	bytes = le64_to_cpu(op->extent.length);
-	read_op = (le32_to_cpu(op->op) == CEPH_OSD_OP_READ);
+	read_op = (le16_to_cpu(op->op) == CEPH_OSD_OP_READ);
 
 	dout("rbd_req_cb bytes=%lld readop=%d rc=%d\n", bytes, read_op, rc);