drm/omap: HDMI: Fix HSW value

On OMAP4 and OMAP5 ES1.0 the HDMI_WP_VIDEO_TIMING_H:HSW field is
set directly to the HSW value. On later SoCs the field needs to be
programmed with the value of HSW-1.

Currently the driver always programs the field with the HSW value. Most
videomodes seem to work fine with that, but at least low resolution
interlaced modes don't work at all.

This patch fixes the HSW for OMAP5 ES2.0+ SoCs.

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