media: i2c: st-mipid02: add usage of v4l2_get_link_freq

Use the helper v4l2_get_link_freq instead of performing manually
check of the LINK_FREQ or PIXELRATE ctrls.

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