vgacon: switch vgacon_scrolldelta() and vgacon_restore_screen()

Switch vgacon_scrolldelta() and vgacon_restore_screen() positions, so
that the former is not needed to be forward-declared.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Helge Deller <deller@gmx.de>