udf: Fix extension of the last extent in the file

udf: Fix extension of the last extent in the file

[ Upstream commit 6bd4ceaacb0eda985596a99afd756e96026e3699 ]

When extending the last extent in the file within the last block, we
wrongly computed the length of the last extent. This is mostly a
cosmetical problem since the extent does not contain any data and the
length will be fixed up by following operations but still.

Fixes: a9cfa2bae782 ("udf: Fix extending file within last block")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>