pca953x: pca953x driver fixes for x86 mrst

Our Moorestown platform has two max7315 chips which is covered by pca953x
i2c gpio driver.

A while ago this driver got updated with nested irq thread support, and it
broke the compatibity with "request_irq".  For example, the gpio_keys.c
driver can not work with this driver now.  This patch fixes the issue by
switching to generic_handle_irq.

Also fix the irq_base issue: irq_base == 0 is valid, and a "-1" value
should mean invalid. IRQ 0 is not a valid IRQ, irq_base of 0 is valid.

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>