media: tuners: fix error return code of hybrid_tuner_request_state()

When kzalloc() fails and state is NULL, no error return code is
assigned.
To fix this bug, __ret is assigned with -ENOMEM in this case.

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>