blockdev: Plug memory leak in drive_uninit()

Started leaking in commit 1dae12e6.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

blockdev.c

@@ -182,6 +182,7 @@ static void drive_uninit(DriveInfo *dinfo)
 {
     qemu_opts_del(dinfo->opts);
     bdrv_delete(dinfo->bdrv);
+    qemu_free(dinfo->id);
     QTAILQ_REMOVE(&drives, dinfo, next);
     qemu_free(dinfo);
 }