[media] media: rc: nuvoton: fix rx fifo overrun handling

To detect a rx fifo overrun it's checked whether the number of elements
in the chip fifo exceeds the fifo size. This check can never return true
and is wrong.
Instead we should generate an interrupt if the fifo overruns.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>