ARM/USB: at91/ohci-at91: remove the use of irq_to_gpio

irq_to_gpio() macro will be removed from AT91 GPIO interrupt
controller. So we replace it with the use of gpio_to_irq()
and a reworked test.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: linux-usb@vger.kernel.org