ext4: Fix ext4_mb_init_cache return error

ext4_mb_init_cache() incorrectly always return EIO on success. This
causes the caller of ext4_mb_init_cache() fail when it checks the return
value.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 6280ad3..d429014 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -809,6 +809,7 @@
 		if (!buffer_uptodate(bh[i]))
 			goto out;
 
+	err = 0;
 	first_block = page->index * blocks_per_page;
 	for (i = 0; i < blocks_per_page; i++) {
 		int group;