powerpc/irq: Improve nanodoc

The OF helpers look like nanodoc but are missing the header. Fix this and a
typo (s/nad/and/) while we are here.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
1 file changed