staging/vme: Fix module parameters

loopback should be declared bool, and variant probably shouldn't be
const.

Signed-off-by: Gerard Snitselaar <dev@snitselaar.org>
Acked-by: Martyn Welch <martyn.welch@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>