ext2: Remove duplicate code from ext2_sync_fs()

Depending in the state (valid or unchecked) of the filesystem either
ext2_sync_super() or ext2_commit_super() is called. If the filesystem is
currently valid (it is checked), we first mark it unchecked and afterwards
duplicate the work that ext2_sync_super() is doing later. Therefore this
patch removes the duplicate code and calls ext2_sync_super() directly after
marking the filesystem unchecked.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Jan Kara <jack@suse.cz>