bus/vdev: fix multi-process IPC buffer leak on scan

bus/vdev: fix multi-process IPC buffer leak on scan

This patch fixes an issue caught with ASAN where a vdev_scan()
to a secondary bus was failing to free some memory.

The doxygen comment in EAL is fixed at the same time.

Fixes: cdb068f031c6 ("bus/vdev: scan by multi-process channel")
Fixes: 783b6e54971d ("eal: add synchronous multi-process communication")
Cc: stable@dpdk.org
Signed-off-by: Paul Luse <paul.e.luse@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>