dm mpath: log device name

Make the mapped device structure accessible to hardware handlers so error
messages can include the device name.

Signed-off-by: Edward Goggin <egoggin@emc.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --cc drivers/md/dm-hw-handler.h
Simple merge

diff --cc drivers/md/dm-mpath.c
Simple merge

diff --cc drivers/md/dm.c
Simple merge