dm exception store: fix init error path

commit aadbe266 upstream.

Call the correct exit function on failure in dm_exception_store_init.

Signed-off-by: Andrei Warkentin <andrey.warkentin@gmail.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>