imx-drm: ipu-common: Check the return value from clk_prepare_enable()

clk_prepare_enable() may fail, so let's check its return value and propagate it
in the case of error.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>