ext4: error proc entry creation when the fs/ext4 is not correctly created

When the directory fs/ext4 is not correctly created under proc, the entry
under this directory should not be created.

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>