re PR tree-optimization/57537 (gcc.dg/vect/slp-widen-mult-half.c generating wrong code on PowerPC64)

	PR tree-optimization/57537
	* tree-vect-patterns.c (vect_recog_widen_mult_pattern): If
	vect_handle_widen_op_by_const, convert oprnd1 to half_type1.

From-SVN: r200000