modedb: fix incorrect sync and vmode flags for CVT modes

The temporary structure for calculated CVT mode is not initialized.  Few
fields have only bits or-ed or and-ed so they may be left in incorrect
(random) state.

Testing of the tridentfb seems like a good exercise for the fbdev layer.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>