gpio/davinci: Use accessor function irq_data_get_irq_handler_data()

This is a preparatory patch for moving irq_data struct members.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>