Missing pointer dereference in tree-affine.c

Missing pointer dereference in tree-affine.c

wide_int_constant_multiple_p used:

          if (*mult_set && mult != 0)
            return false;

to check whether we had previously seen a nonzero multiple, but "mult" is
a pointer to the previous value rather than the previous value itself.

Noticed by inspection while working on another patch, so I don't have a
testcase.  I tried adding an assert for combinations that were wrongly
rejected before but it didn't trigger during a bootstrap and regtest.

Tested on x86_64-linux-gnu.

gcc/
	* tree-affine.c (wide_int_constant_multiple_p): Add missing
	pointer dereference.

From-SVN: r236040