vt8623fb: change option mode to mode_option

Change the option "mode" into "mode_option".

This is one step toward changing all fb drivers to have common "mode_option"
parameter.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>