video: mxsfb: fix pixel clock polarity

video: mxsfb: fix pixel clock polarity

DISPLAY_FLAGS_PIXDATA_NEGEDGE means the controller drives the data on
pixel clocks falling edge. That is DOTCLK_POL=0 (default) not 1.

The mxsfb-drm driver in the Linux kernel has made the same change and it
remains to this day:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.19-rc2&id=53990e416bb7adaa59d045f325a47f31a11b75ee

I found this was required on an IMX8X SoM.

Without the patch a splash screen displays with aliasing-like jagged edges.

Signed-off-by: Sam Meredith <sam@aandtinstruments.com>
[fabio: Put more information into the commit log]
Signed-off-by: Fabio Estevam <festevam@gmail.com>