isl_union_*_mul_isl_int: add missing &-operator

isl_union_*_mul_isl_int: add missing &-operator

When using GMP as integer implementation, isl_int is effectively
declared as __mpz_struct isl_int[1]. This will cause an automatic
decay-to-pointer in various contexts. Using IMath, isl_int is already
declared as pointer and forgetting the address-of operator will result
in a pointer to IMath's internal data structure instead.  Later code
will try to double-dereference, which most probably will result in a
segmentation fault.

This problem was fixed before in b9c7b8c (isl_union_*_mul_isl_int:
pass address of isl_int to callback, Sat Sep 21 14:15:36 2013 +0200),
but was somehow reintroduced in f245643 (isl_union_templ.c: allow
multiple inclusion, Sat Aug 24 14:17:46 2013 +0200).

Signed-off-by: Michael Kruse <isl@meinersbur.de>
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>