fbdev: uvesafb: Remove uvesafb_exec() prototype from include/video/uvesafb.h

uvesafb_exec() is a static function defined and called only in
drivers/video/fbdev/uvesafb.c, remove the prototype from
include/video/uvesafb.h.

Fixes the warning:
./include/video/uvesafb.h:112:12: warning: 'uvesafb_exec' declared 'static' but never defined [-Wunused-function]
when including '<video/uvesafb.h>' in an external program.

Signed-off-by: Jorge Maidana <jorgem.linux@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>