dm cache: set needs_check flag after aborting metadata

Otherwise the commit that will be aborted will be associated with the
metadata objects that will be torn down.  Must write needs_check flag
to metadata with a reset block manager.

Found through code-inspection (and compared against dm-thin.c).

Cc: stable@vger.kernel.org
Fixes: 028ae9f7

 ("dm cache: add fail io mode and needs_check flag")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>