btrfs/286: add missing calls to _scratch_dev_pool_put and _spare_dev_put

btrfs/286: add missing calls to _scratch_dev_pool_put and _spare_dev_put

The test is doing a _scratch_dev_pool_get, which shrinks the list of
devices in SCRATCH_DEV_POOL, but it's not calling _scratch_dev_pool_put
before it finishes. This will result in subsequent tests (none at the
moment however) getting a reduced list of devices in SCRATCH_DEV_POOL.

The same goes for the spare device, the test calls _spare_dev_get but
it never calls _spare_dev_put.

So add the missing calls.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>