OMAPDSS: Take pixelclock unit change into account in hdmi_compute_acr()

Pixelclock unit change from kHz to Hz should be taken into account
in CTS value calculations in hdmi_compute_acr().

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>