iio: adc: palmas_gpadc: fix NULL dereference on rmmod

stable inclusion
from stable-v5.10.180
commit f5e96af71eab491a19fb3926ab42d592118ca52c
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8DDFN

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5e96af71eab491a19fb3926ab42d592118ca52c



--------------------------------

[ Upstream commit 49f76c49 ]

Calling dev_to_iio_dev() on a platform device pointer is undefined and
will make adc NULL.

Signed-off-by: Patrik Dahlström <risca@dalakolonin.se>
Link: https://lore.kernel.org/r/20230313205029.1881745-1-risca@dalakolonin.se


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>