Remove unnecessary code in ep93xx_gpio_ab_irq_handler().

The desc calculation for gpio port B was left in when the following
commit was merged.

commit d8aa0251
Author: Dmitry Baryshkov <dbaryshkov@gmail.com>
Date:   Thu Oct 9 13:36:24 2008 +0100

    [ARM] 5298/1: Drop desc_handle_irq()

It's not needed so remove it.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>