iomap: micro optimize the ki_pos assignment in iomap_file_buffered_write

We have the new value for ki_pos right at hand in iter.pos, so assign
that instead of recalculating it from ret.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.harjani@gmail.com>

Author: Christoph Hellwig

fs/iomap/buffered-io.c

@@ -875,7 +875,7 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
 	if (unlikely(iter.pos == iocb->ki_pos))
 		return ret;
 	ret = iter.pos - iocb->ki_pos;
-	iocb->ki_pos += ret;
+	iocb->ki_pos = iter.pos;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);