media: adv7604.c: add missing return

A 'return' was missing when detecting Arbitration Lost and
calling transmit_done. With the return transmit_done could be
called a second time, confusing the CEC framework. Luckily
the Arbitration Lost condition is very rare.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>