dm: add missing unlock on in dm_keyslot_evict()

commit 650266ac upstream.

We need to call dm_put_live_table() even if dm_get_live_table() returns
NULL.

Fixes: 9355a9eb ("dm: support key eviction from keyslot managers of underlying devices")
Cc: stable@vger.kernel.org	# v5.12+
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>