xpsice, fix premature tfree() invocation

reported by "Heini X" on the ngspice-users mailing list

this bug was introduced in

: commit 0af75f3bd9
: Date:   Sat Aug 18 18:31:23 2012 +0200
:
:     subckt.c, mif_inp2.c: plug XSPICE setup memory leaks

src/xspice/mif/mif_inp2.c

@@ -746,9 +746,6 @@ MIFget_port_type(
 
         *status = MIF_OK;
     }
-
-    if (temp)
-        tfree(temp);
 }