fs/ext4/fsync.c: generic_file_fsync call based on barrier flag

fs/ext4/fsync.c: generic_file_fsync call based on barrier flag

generic_file_fsync has been updated to issue a flush for older
filesystems.

This patch tests for barrier flag in ext4 mount flags and calls the right
function.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>