ext4: Use generic_buffers_fsync_noflush() implementation

ext4 when got converted to iomap for dio, it copied __generic_file_fsync
implementation to avoid taking inode_lock in order to avoid any deadlock
(since iomap takes an inode_lock while calling generic_write_sync()).

The previous patch already added generic_buffers_fsync*() which does not
take any inode_lock(). Hence kill the redundant code and use
generic_buffers_fsync_noflush() function instead.

Tested-by: Disha Goel <disgoel@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <b43d4bb4403061ed86510c9587673e30a461ba14.1682069716.git.ritesh.list@gmail.com>