uvesafb: fix warnings about unused variables on non-x86

Variables that are only used in #ifdef CONFIG_X86 should also only be
declared there.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.de>
Cc: Michal Januszewski <spock@gentoo.org>
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>