thor: defer parsing of device string to IO backend

Commit d4f5ef59cc7 "dfu: defer parsing of device string to IO backend" changed
the function signature of dfu_init_env_entities(). Adjust cmd_thordown.c
to match that change.

Also, apply the same change as commit d6d37d737b58e "dfu: free entities
when parsing fails" to cmd_thordown.c.

Fixes: d4f5ef59cc7 ("dfu: defer parsing of device string to IO backend")
Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>