gpio: dwapb: drop irq_setup_generic_chip()

The driver calls irq_alloc_domain_generic_chips() which creates a gc and
adds it to gc_list. The driver later then calls irq_setup_generic_chip()
which also initializes the gc and adds it to the gc_list() and this
corrupts the list. Enable LIST_DEBUG and you see the kernel complain.
This isn't required, irq_alloc_domain_generic_chips() did the init.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Alan Tull <delicious.quinoa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>