ext4: use ext4_write_inode() when fsyncing w/o a journal

In no-journal mode, we previously used __generic_file_fsync() in
no-journal mode.  This triggers a lockdep warning, and in addition,
it's not safe to depend on the inode writeback mechanism in the case
ext4.  We can solve both problems by calling ext4_write_inode()
directly.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org