gpio: pca953x: Fix uninitialized pending variable

When pca953x_irq_pending returns false, the pending parameter won't
be set. But pca953x_irq_handler continues using this uninitialized
variable as pending irqs and will cause problem.
Fix the issue by initializing pending to 0.

Fixes: 064c73af ("gpio: pca953x: Synchronize interrupt handler properly")
Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>