media: tegra-cec: fix cec_notifier_parse_hdmi_phandle return check

cec_notifier_parse_hdmi_phandle returns an error pointer, not a NULL
pointer on error.

Fixes: 4d34c926: ("media: tegra_cec: use new cec_notifier_parse_hdmi_phandle helper")

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>