vmci_host: get rid of pointless access_ok()

get_user_pages_fast() doesn't need the caller to check that.
NB: reachable only from ioctl(2) and only under USER_DS

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>