cc2538: gpio: Fix missed interrupts
cc2538: gpio: Fix missed interrupts

Only the interrupt flags that have been handled must be cleared.
Otherwise, if a new interrupt occurs after the interrupt statuses are
read and before they are cleared, then it is discarded without having
been handled. This issue was particularly likely with two interrupt
trigger conditions occurring on different pins of the same port in a
short period of time.

Signed-off-by: Benoît Thébaudeau <b3efeb72fa9d3102885911404c5fbece843f6c8f@gmail.com>

arurke/contiki,bluerover/6lbr,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki