ENGR00182769 HDMI: No sound when playing audio in 480p mode

ENGR00182769 HDMI: No sound when playing audio in 480p mode

It is cause by HDMI audio driver can't get right pixel clock
from IPU driver if pixel clock source from HSP clock not from
DI clock.
HDMI driver get pixel clock by call clk_get_rate() function,
but the function return actually clock, in some videomode the
actually pixel clock is not right equal the pixel clock in CEA spec.

Get pixel clock from video mode struct instead of CCM register.
480P HDMI audio can work.

Signed-off-by: Sandor Yu <R01008@freescale.com>