gpio: xilinx: No need to disable IRQs in the handler

In IRQ handler interrupts are already disabled, hence no need
to repeat it. Even in the threaded case, it is not a problem
because IRQ framework keeps interrupt disabled there as well.
Remove disabling IRQ part in the handler.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Neeli Srinivas <sneeli@xilinx.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>