media: i2c: mt9v111: Fix v4l2-ctrl error handling

Fix error handling of v4l2_ctrl creation by inspecting the ctrl.error flag
instead of testing for each returned value correctness.

As reported by Dan Carpenter returning PTR_ERR() on the v4l2_ctrl_new_std()
return value is also wrong, as that function return NULL on error.

While at there re-order the cleanup path to respect the operation inverse
order.

Fixes: aab7ed1c

 "media: i2c: Add driver for Aptina MT9V111"
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>