uvesafb: Correct/simplify warning message

Streamline it a bit. No functional change.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Wang YanQing <udknight@gmail.com>
Cc: Michal Januszewski <spock@gentoo.org>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Acked-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>