staging: vboxvideo: Kconfig: Fix typos in help text

This fixes typos in vboxvideo's help text. Most notably, "to builtin
this module" becomes "to build this driver built-in to the kernel".

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>