thunderbolt: Fix memory leak if ida_simple_get() fails in enumerate_services()

The svc->key field is not released as it should be if ida_simple_get()
fails so fix that.

Fixes: 9aabb685 ("thunderbolt: Fix to check return value of ida_simple_get")
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>