media: radio-si476x: Remove the unneeded result variable

Return the value v4l2_fh_release() directly instead of storing it in
another redundant variable.

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