mtd: docg3: dereferencing an ERR_PTR() in docg3_probe()

If doc_probe_device() returned an ERR_PTR, then we accidentally saved
that to docg3_floors[floor] = mtd; which gets derefenced in the error
handling when we call doc_release_device().

I've reworked the error handling to take care of that and hopefully
make it a little simpler.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/devices/docg3.c

@@ -2027,21 +2027,24 @@ static int __init docg3_probe(struct platform_device *pdev)
 	if (!docg3_bch)
 		goto nomem2;
 
-	ret = 0;
 	for (floor = 0; floor < DOC_MAX_NBFLOORS; floor++) {
 		mtd = doc_probe_device(base, floor, dev);
-		if (floor == 0 && !mtd)
-			goto notfound;
-		if (!IS_ERR_OR_NULL(mtd))
-			ret = mtd_device_parse_register(mtd, part_probes,
-							NULL, NULL, 0);
-		else
+		if (IS_ERR(mtd)) {
 			ret = PTR_ERR(mtd);
+			goto err_probe;
+		}
+		if (!mtd) {
+			if (floor == 0)
+				goto notfound;
+			else
+				continue;
+		}
 		docg3_floors[floor] = mtd;
+		ret = mtd_device_parse_register(mtd, part_probes, NULL, NULL,
+						0);
 		if (ret)
 			goto err_probe;
-		if (mtd)
-			found++;
+		found++;
 	}
 
 	ret = doc_register_sysfs(pdev, docg3_floors);