config: Invoke mktemp(1) without parameters.

This increases portability because some mktemp implementations do
not support -t flag. Calling mktemp without parameters creates temp
files in $TMPDIR or /tmp which was the reason -t was used in the
first place.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8580 4b0bc96b-bc66-0410-9d44-ebda105a78c1