media: i2c: ds90ub960: Fix uninitialized variable in ub960_rxport_bc_ser_config()

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

Fixes: e2a3b695 ("media: i2c: ds90ub960: Configure serializer using back-channel")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Jai Luthra <jai.luthra@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>