media/radio: Make radio_isa_common_remove() return void

Instead of an unconditional return 0, return no value. One of the two
callers ignored the return value already before.

This simplifies the next patch.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Link: https://lore.kernel.org/r/20210122092449.426097-3-uwe@kleine-koenig.org


Signed-off-by: Takashi Iwai <tiwai@suse.de>