drivers: gpio: mspm0: Mask interrupts correctly

Reading back the raw interrupt status from the gpio controller, provides
the interrupt mask _without_ the controller's masking registers applied.
This means that e.g. a rising edge would trigger an interrupt even on
pins that are configured for falling edge only.

Fix this by reading the "enabled" interrupt status instead of the raw
one.

Signed-off-by: Emil Dahl Juhl <emdj@bang-olufsen.dk>