video: ipu_disp: remove pixclk fixup

The ipu display insists on having a lower_margin smaller
then 2. If this is not the case it will attempt to force
it and adjust the pixclk accordingly. This multiplies pixclk
in Hz with the width and height, since this is typically
a * 10^7 * b * 10^2 * c * 10^2 this will overflow the
uint_32 and make things even worse. Since this is a
bootloader and the adjustment is neglectible, just force
it to two and warn about it.

Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>