staging/nvec: Use platform_get_irq()

As opposed to platform_get_resource(), the platform_get_irq() function
has special code to handle driver probe deferral when booting using DT
and where an interrupt provider hasn't been registered yet. While this
is unlikely to become an issue for nvec, platform_get_irq() is the
recommended way to get at interrupts.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>