staging: vt6656: Return on isr0 when zero.

When isr0 is zero there is nothing more todo so return and
pull following code in.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/8dccc74d-d0bb-e8e7-df81-dfd81e3fd7d8@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>