media: i2c: imx258: add missing mutex protection for format code access

media: i2c: imx258: add missing mutex protection for format code access

imx258_open(), imx258_enum_mbus_code(), and imx258_enum_frame_size()
call imx258_get_format_code() without holding imx258->mutex. However,
imx258_get_format_code() has lockdep_assert_held(&imx258->mutex)
indicating that callers must hold this lock.

All other callers of imx258_get_format_code() properly acquire the mutex:
- imx258_set_pad_format() acquires mutex at imx258.c:918
- imx258_get_pad_format() acquires mutex at imx258.c:896

The mutex is needed to protect access to imx258->vflip->val and
imx258->hflip->val which are used to calculate the bayer format code.

Add mutex_lock()/mutex_unlock() around the imx258_get_format_code()
calls in the affected functions to fix the missing lock protection.

Signed-off-by: Ziyi Guo <n7l8m4@u.northwestern.edu>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>