irqchip: nvic: Fix wrong num_ct argument for irq_alloc_domain_generic_chips()

The third parameter of irq_alloc_domain_generic_chips() is the number of
irq_chip_type instances associated with these chips rather than numbanks.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Cc: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: kernel@pengutronix.de
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>