pinctrl: sunxi: Mark the irq bank not found in sunxi_pinctrl_irq_handler() with WARN_ON

The interrupt descriptor cannot be found in the interrupt processing
function, and this situation cannot happen when the system is running
normally. It doesn't seem right to return directly to the status of not
handling gic. In this case, it must be a bug, let's mark it with
WARN_ON.

Signed-off-by: Yangtao Li <frank@allwinnertech.com>
Link: https://lore.kernel.org/r/470ebae22fc5434ad5409c4f6e29255467b3cef6.1604988979.git.frank@allwinnertech.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>