drm/fsl-dcu: disable clock on error path

In fsl_dcu_drm_pm_resume() we should disable the previously enabled
clock (fsl_dev->clk) when enabling fsl_dev->pix_clk fails.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>