examples/vhost_scsi: fix header check for meson build

examples/vhost_scsi: fix header check for meson build

The header check for the example app was looking for virtio_scsi.h without
the "linux/" prefix, which meant it was never getting found when it should
have been.

Fixes: 8d47a753b7cb ("examples/vhost_scsi: disable build if missing dependency")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>