drm/omap: dsi: fix compile errors when enabling debug prints

dsi.c compile fails if PRINT_VERBOSE_VM_TIMINGS is enabled, as the
video timings were not converted in the code behind that ifdef. Note
that PRINT_VERBOSE_VM_TIMINGS has to be enabled by hand, there's no
config option for it.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
[tomi.valkeinen@ti.com: fixed the patch description]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>