drm/omap: omap_display_timings: rename hsw to hsync_len

In preparation to move the stack to use the generic videmode struct for
display timing information rename the hsw member to hsync_len.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>