media: i2c: st-mipid02: don't keep track of streaming status

As explained in the following series, subdev do not have to keep
track of their streaming status:

https://lore.kernel.org/linux-media/20230914181704.4811-1-laurent.pinchart@ideasonboard.com/



Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
[Sakari Ailus: Remove redundant local variable in mipid02_set_fmt.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>