V4L/DVB (8790): saa7115: call i2c_set_clientdata only when state != NULL

Not a bug as such, but it looks really strange doing this before
checking whether the state structure could be allocated.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>