Staging: ipack/devices/ipoctal: acknowledge BREAK condition.

Clear the BREAK flag from the ISR register. Doing that, we avoid to read
the same condition for the next character received.

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