gpio/lynxpoint: check if the interrupt is enabled in IRQ handler

Checking LP_INT_STAT is not enough in the interrupt handler because its
contents get updated regardless of whether the pin has interrupt enabled or
not. This causes the driver to loop forever for GPIOs that are pulled up.

Fix this by checking the interrupt enable bit for the pin as well.

Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>