fbdev: sh-mobile: restore display size configuration

An earlier patch replaced open-coded video-mode configuration from
platform data by a call to fb_videomode_to_var(), thereby setting
ofdisplay sizes have been accidentally lost. Restore them.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>