gpu: host1x: Fix a memory leak in 'host1x_remove()'

Add a missing 'host1x_channel_list_free()' call in the remove function,
as already done in the error handling path of the probe function.

Fixes: 8474b025 ("gpu: host1x: Refactor channel allocation code")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Thierry Reding <treding@nvidia.com>