ext2: Fix ki_pos update for DIO buffered-io fallback case

ext2: Fix ki_pos update for DIO buffered-io fallback case

Commit "filemap: update ki_pos in generic_perform_write", made updating
of ki_pos into common code in generic_perform_write() function.
This also causes generic/091 to fail.
This happened due to an in-flight collision with:
fb5de4358e1a ("ext2: Move direct-io to use iomap"). I have chosen fixes tag
based on which commit got landed later to upstream kernel.

Fixes: 182c25e9c157 ("filemap: update ki_pos in generic_perform_write")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <d595bee9f2475ed0e8a2e7fb94f7afc2c6ffc36a.1700643443.git.ritesh.list@gmail.com>