media: i2c: imx334: uninitialized variable in imx334_update_exp_gain()

The "ret" variable is not initialized on the success path.  Set it to
zero.

Fixes: 7b19b0fc ("media: i2c: imx334: Convert to CCI register access helpers")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>