Use the provided function rather than re-coding this bit of code.
This also gets us protection against using these functions from
invalid contexts.
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>