ipack/devices/ipoctal: ack IRQ before processing it

Due to the IRQ processing, we can generate another IRQ that can come before we
end the previous one, so we lost it. E.g. when transmitting a character.

To allow the processing in SMP machines, we ack the IRQ at the beginning of the
IRQ handler.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>