uvesafb: fix selecting mode with the vbemode option

If the vbemode option is used, uvesafb calls fb_get_mode() without first
setting the resolution in info->var.  This results in a division by zero
in fb_get_mode(), as evidenced e.g.  in [1].  Fix this by ensuring the
info->var structure is populated before fb_get_mode() is called.

[1] http://bugzilla.kernel.org/show_bug.cgi?id=11661#c37

Signed-off-by: Michal Januszewski <spock@gentoo.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>