drbd: don't expose failed local READ to upper layers

fix regression introduced in 8.3.3:
 commit a9b17323f2875f5d9b132c2b476a750bf44b10c7
 Author: Lars Ellenberg <lars.ellenberg@linbit.com>
 Date:   Wed Aug 12 15:18:33 2009 +0200

     out-of-spinlock completion of master bio

 : (bio_rw(bio) == READA)
    ? read_completed_with_error
    : read_ahead_completed_with_error;

is obviously not what was intended.

No one noticed because of
 * page-cache at work,
 * local RAIDs

Impact:
Failed local READs are not retried remotely,
but errored to upper layers, causing filesystems
to remount read-only, or worse.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_worker.c

@@ -235,7 +235,7 @@ void drbd_endio_pri(struct bio *bio, int error)
 	if (unlikely(error)) {
 		what = (bio_data_dir(bio) == WRITE)
 			? write_completed_with_error
-			: (bio_rw(bio) == READA)
+			: (bio_rw(bio) == READ)
 			  ? read_completed_with_error
 			  : read_ahead_completed_with_error;
 	} else