Staging: vme/tsi148: Depend on VIRT_TO_BUS

This driver depends on virt_to_bus working correctly, but it doesn't
exist on ppc64 (and probably other arches).

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>