ext2: Use generic_buffers_fsync() implementation

ext2: Use generic_buffers_fsync() implementation

Next patch converts ext2 to use iomap interface for DIO.
iomap layer can call generic_write_sync() -> ext2_fsync() from
iomap_dio_complete while still holding the inode_lock().

Now writeback from other paths doesn't need inode_lock().
It seems there is also no need of an inode_lock() for
sync_mapping_buffers(). It uses it's own mapping->private_lock
for it's buffer list handling.
Hence this patch is in preparation to move ext2 to iomap.
This uses generic_buffers_fsync() which does not take any inode_lock()
in ext2_fsync().

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: <76d206a464574ff91db25bc9e43479b51ca7e307.1682069716.git.ritesh.list@gmail.com>