gpio/langwell: re-read the IRQ status register after each iteration

The IRQ status register should be re-read after each iteration.
Otherwise the loop misses the interrupt if it gets raised immediately
after handled.

Reported-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>