ext4: mark inode dirty after converting inline directory

If ext4_convert_inline_data() was called on a directory with inline
data, the filesystem was left in an inconsistent state (as considered by
e2fsck) because the file size was not increased to cover the new block.
This happened because the inode was not marked dirty after i_disksize
was updated.  Fix this by marking the inode dirty at the end of
ext4_finish_convert_inline_dir().

This bug was probably not noticed before because most users mark the
inode dirty afterwards for other reasons.  But if userspace executed
FS_IOC_SET_ENCRYPTION_POLICY with invalid parameters, as exercised by
'kvm-xfstests -c adv generic/396', then the inode was never marked dirty
after updating i_disksize.

Cc: stable@vger.kernel.org  # 3.10+
Fixes: 3c47d541
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>