It's possible to hit a race condition if interrupts are generated on a GPIO
pin when the IRQ line in question is being disabled.

If the interrupt is freed, bcm2835_gpio_irq_disable() is called which
disables the event generation sources (edge, level). If an event occurred
between the last disabling of hard IRQs and the write to the event
source registers, a bit would be set in the GPIO event detect register
(GPEDSn) which goes unacknowledged by bcm2835_gpio_irq_handler()
so Linux complains loudly.

There is no per-GPIO mask register, so when disabling GPIO interrupts
write 1 to the relevant bit in GPEDSn to clear out any stale events.
Signed-off-by: Jonathan Bell <jonathan@raspberrypi.org>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>