media: i2c: st-mipid02: use active state to store pad formats

Store formats information within pad allowing to simplify further more
the driver (mutex / format store within the driver structure no more
necessary).

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
[Sakari Ailus: Address init_cfg -> init_state API change.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>