drm/gma500/psb: Actually use VBT mode when it is found

drm/gma500/psb: Actually use VBT mode when it is found

commit 82bc9a42cf854fdf63155759c0aa790bd1f361b0 upstream.

With LVDS we were incorrectly picking the pre-programmed mode instead of
the prefered mode provided by VBT. Make sure we pick the VBT mode if
one is provided. It is likely that the mode read-out code is still wrong
but this patch fixes the immediate problem on most machines.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78562
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170418114332.12183-1-patrik.r.jakobsson@gmail.com
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>