UBI: fix double free on error path

If we fail in 'ubi_eba_init_scan()', we free
'ubi->volumes[i]->eba_tbl' in there, but also later free it
in 'free_internal_volumes()'. Fix this by assigning NULL
to 'ubi->volumes[i]->eba_tbl' after it is freed.

Signed-off-by: Adrian Hunter <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/eba.c

···
 		if (!ubi->volumes[i])
 			continue;
 		kfree(ubi->volumes[i]->eba_tbl);
+		ubi->volumes[i]->eba_tbl = NULL;
 	}
 	return err;
 }