media: i2c: tda1997x: prevent potential NULL pointer access

i2c_new_dummy() can fail returning a NULL pointer. This is not checked
and the returned pointer is blindly used. Convert to
devm_i2c_new_dummy_client() which returns an ERR_PTR and also add a
validity check. Using devm_* here also fixes a leak because the dummy
client was not released in the probe error path.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>