media: i2c: ov7670: 0 instead of -EINVAL was returned

If the media bus is unsupported, then return -EINVAL. Instead it
returned 'ret' which happened to be 0.

This fixes a smatch warning:

ov7670.c:1843 ov7670_parse_dt() warn: missing error code? 'ret'

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: 01b84448 ("media: v4l2: i2c: ov7670: Implement OF mbus configuration")
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>