commit befa6011 upstream.

In order to make the driver work with the common clock framework, this
patch converts the clk_enable()/clk_disable() to
clk_prepare_enable()/clk_disable_unprepare().

Also add error checking for clk_prepare_enable().
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>