drivers: block: Mark functions as static in drbd_req.c

Mark functions drbd_request_prepare() and find_oldest_request() as
static in drbd/drbd_req.c because they are not used outside this file.

This eliminates the following warnings in drbd/drbd_req.c:
drivers/block/drbd/drbd_req.c:1037:1: warning: no previous prototype for ‘drbd_request_prepare’ [-Wmissing-prototypes]
drivers/block/drbd/drbd_req.c:1323:22: warning: no previous prototype for ‘find_oldest_request’ [-Wmissing-prototypes]
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>

drivers/block/drbd/drbd_req.c

@@ -1033,7 +1033,7 @@ static void drbd_queue_write(struct drbd_conf *mdev, struct drbd_request *req)
  * request on the submitter thread.
  * Returns ERR_PTR(-ENOMEM) if we cannot allocate a drbd_request.
  */
-struct drbd_request *
+static struct drbd_request *
 drbd_request_prepare(struct drbd_conf *mdev, struct bio *bio, unsigned long start_time)
 {
 	const int rw = bio_data_dir(bio);
@@ -1320,7 +1320,7 @@ int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct
 	return limit;
 }
 
-struct drbd_request *find_oldest_request(struct drbd_tconn *tconn)
+static struct drbd_request *find_oldest_request(struct drbd_tconn *tconn)
 {
 	/* Walk the transfer log,
 	 * and find the oldest not yet completed request */