debugfs: Fix statfs() regression in 3.2.69

Commit 915f4f86ddc4 ("debugfs: leave freeing a symlink body until inode
eviction", commit 0db59e59299f upstream) changed debugfs to define its
own super_operations and implement the evict_inode operation.

Luis Henriques pointed out that it needs to define the statfs
operation, as in simple_super_operations which it was using before.

Reported-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc fs/debugfs/inode.c
Simple merge