Documentation: fix the now deprecated reference to {set,reset}_scoop_gpio

Due to recent patches removing the now deprecated references to
{set,reset}_scoop_gpio() and converting them to the generic GPIO
API, the references in the documentation also need to be fixed.

Signed-off-by: Eric Miao <eric.miao@marvell.com>
Cc: Liam Girdwood <lrg@kernel.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>