gpio: tegra: fix unbalanced chained_irq_enter/exit

When more than one GPIO IRQs are triggered simultaneously,
tegra_gpio_irq_handler() called chained_irq_exit() multiple
times for one chained_irq_enter().

Fixes: 3c92db9a


Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
[Also changed the variable to a bool]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>