media: video-i2c: hwmon: fix return value from amg88xx_hwmon_init()

PTR_ERR was making any pointer passed an error pointer, and should be
replaced with PTR_ERR_OR_ZERO which checks if is an actual error condition.

Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>