dm table: rework reference counting fix

Fix an error introduced in dm-table-rework-reference-counting.patch.

When there is failure after table initialization, we need to use
dm_table_destroy, not dm_table_put, to free the table.

dm_table_put may be used only after dm_table_get.

Cc: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Jonathan Brassow <jbrassow@redhat.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>