media: i2c: ds90ub960: Fix missing return check on ub960_rxport_read call

The function ub960_rxport_read is being called and afterwards ret is
being checked for any failures, however ret is not being assigned to
the return of the function call. Fix this by assigning ret to the
return of the call which appears to be missing.

Fixes: afe267f2 ("media: i2c: add DS90UB960 driver")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>