Staging: unisys: virthba: Add dependency on SCSI

If CONFIG_SCSI is not enabled, compiling virthba.c goes horribly wrong with
undefined symbols.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>