gpio: omap: Remove unnecessary lockdep class

GPIO irqchips assign to the cascaded IRQs their own lock class
in order to avoid warnings about lockdep recursions since that
allow the lockdep core to keep track of things.

Since commit e45d1c80 ("gpio: put GPIO IRQs into their own lock class")
there is no need to do this in a driver if it's using the GPIO
irqchip helpers since gpiolib already assigns a lockdep class.

Signed-off-by: Javier Martinez Canillas <jmartinez@softcrates.net>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>