GPIO fixes for the v4.7 cycle: - It was discovered that too many parts of the kernel does not respect gpiod_to_irq() returning zero for an invalid IRQ. While this gets fixed, we need to make it return negative errorcodes again. - Harden the library a bit when passed error pointers. It is a bug to use these, but let's be helpful and warn the users. - Fix an uninitialized spinlock in the 104-idi-48 driver.