[PATCH] ufs: truncate negative to unsigned fix

During ufs_trunc_direct which is subroutine of ufs::truncate, we try the first
of all free parts of block and then whole blocks.  But we calculate size of
block's part to free in the wrong way.

This may cause bad update of used blocks and fragments statistic, and you can
got report that you have free 32T on 1Gb partition.

Signed-off-by: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>