gpio: pcie-idio-24: Fix irq mask when masking

Fix the bitwise operation to remove only the corresponding bit from the
mask.

Fixes: 58556204 ("gpio: Add GPIO support for the ACCES PCIe-IDIO-24 family")
Cc: stable@vger.kernel.org
Signed-off-by: Arnaud de Turckheim <quarium@gmail.com>
Reviewed-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>