UBI: fix error return code

Set the return variable to an error code as done elsewhere in the function.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}

// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: Richard Weinberger <richard@nod.at>
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index e05dc62..57deae9 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1245,8 +1245,10 @@
 	ubi_wl_entry_slab = kmem_cache_create("ubi_wl_entry_slab",
 					      sizeof(struct ubi_wl_entry),
 					      0, 0, NULL);
-	if (!ubi_wl_entry_slab)
+	if (!ubi_wl_entry_slab) {
+		err = -ENOMEM;
 		goto out_dev_unreg;
+	}
 
 	err = ubi_debugfs_init();
 	if (err)