media: cec-gpio: drop the cec_gpio_free callback

Since the CEC pin framework now keeps track of the interrupt
and calls disable_irq when the kthread stops, there is no
longer any need for the cec-gpio driver to do this in the
free callback. So drop this code.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>