imx-drm: imx-hdmi: fix CTS/N setup at init time

Many of the variables for the audio clock regenerator (CTS/N) were not
initialised in any way.  The pixel rate which was being used also
wasn't being adjusted at all when the display mode is modified.

Get rid of the seaprate 'pixel_clk_rate', and use the stored pixel
clock rate instead.  Pass this desired pixel clock rate into
hdmi_set_clk_regenerator().  Collapse down hdmi_init_clk_regenerator()
since it is a copy of hdmi_set_clk_regenerator(), and pass a default
pixel clock rate.

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>