video/omap: remove mux.h include

Including mux.h should no longer be needed for omap2/3/4 SoCs
outside arch/arm/mach-omap2 files.

Signed-off-by: Nicolas Kaiser <nikai@nikai.net>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>