ext4: fix checks for data=ordered and journal_async_commit options

Combination of data=ordered mode and journal_async_commit mount option
is invalid. However the check in parse_options() fails to detect the
case where we simply end up defaulting to data=ordered mode and we
detect the problem only on remount which triggers hard to understand
failure to remount the filesystem.

Fix the checking of mount options to take into account also the default
mode by moving the check somewhat later in the mount sequence.

Reported-by: Wolfgang Walter <linux@stwm.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>