media: i2c: et8ek8: Drop support for per-mode external clock frequency

media: i2c: et8ek8: Drop support for per-mode external clock frequency

The et8ek8 driver supports programming different external clock
frequencies for different modes, but in practice all modes use a 9.6MHz
external clock. Drop support for this feature and use a hardcoded
frequency, in preparation for further refactoring of external clock
handling.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>