drivers: gpio_cmsdk_ahb: Fix erronous if statements

The GPIO_INT_LEVEL and GPIO_INT_ACTIVE_LOW values are  zero so the
statements are never executed then is better use the bit complement
masks

This issue was reported by Coverity

Coverity-CID: 157586

Change-Id: Ic8b20660a991dd3d0c71248f84c917e5ce5c3c7c
Signed-off-by: Sergio Rodriguez <sergio.sf.rodriguez@intel.com>