dm cache: replace memcpy with struct assignment

Use struct assignment rather than memcpy in dm cache.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

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

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