tree-optimization/113552 - fix num_call accounting in simd clone vectorization

tree-optimization/113552 - fix num_call accounting in simd clone vectorization

The following avoids using exact_log2 on the number of SIMD clone calls
to be emitted when vectorizing calls since that can easily be not
a power of two in which case it will return -1.  For different simd
clones the number of calls will differ by a multiply with a power of two
only so using floor_log2 is good enough here.

	PR tree-optimization/113552
	* tree-vect-stmts.cc (vectorizable_simd_clone_call): Use
	floor_log2 instead of exact_log2 on the number of calls.