util: Avoid localised underflow

util: Avoid localised underflow

Avoid parenthesising an unsigned subtraction that can be negative and,
therefore, underflow.  There is no need for the parentheses and
removing them results in an expression that is evaluated left-to-right
and can not underflow.

It isn't clear that the underflow matters.  lp <= ls, so if (li - lp)
underflows then ls + (li - lp) will always overflow.  This should
produce the correct answer.  However, depending on this seems wrong.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>