MD RAID10: Fix oops when creating RAID10 arrays via dm-raid.c

Commit 2863b9eb didn't take into account the changes to add TRIM support to
RAID10 (commit 532a2a3f).  That is, when using dm-raid.c to create the
RAID10 arrays, there is no mddev->gendisk or mddev->queue.  The code added
to support TRIM simply assumes that mddev->queue is available without
checking.  The result is an oops any time dm-raid.c attempts to create a
RAID10 device.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>