driver:pca953x: Disable input latching for level interrupts

For level interrupts, the latching of the inputs is rather unwanted. The
latching might lead to false interrupt states which occur if the input changes
again before the interrupt is completely processed. This can either be
resolved by reading the input status register twice or by disabling the
latching for level interrupt pins. Without the latching, very short level
interrupt changes are ignored. Since we don't want them anyway, we opt for
the second solution.