[Drbd-dev] Avoid compiler warning about non-bool in logical expression

[David Butterfield]

Avoid a compiler warning:
    drbd_receiver.c:1693:12: warning: logical ‘and’ applied to non-boolean constant [-Wlogical-op]

diff --git a/drbd/drbd_receiver.c b/drbd/drbd_receiver.c
@@ -1690,7 +1690,7 @@ next_bio:
                bio->bi_next = NULL;

                /* strip off REQ_UNPLUG unless it is the last bio */
-               if (bios && DRBD_REQ_UNPLUG)
+               if (bios && (DRBD_REQ_UNPLUG != 0))
                        bio->bi_opf &= ~DRBD_REQ_UNPLUG;
                drbd_generic_make_request(device, fault_type, bio);