ARM: 7800/1: ARMv7-M: Fix name of NVIC handler function

The name changed in response to review comments for the nvic irqchip
driver when the original name was already accepted into Russell King's
tree.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>