[DAGCombiner][TargetLowering] Pass SDValue by value to isMulAddWithConstProfitable.

Internally to DAGCombiner the SDValues were passed by non-const
reference despite not being modified. They were then passed by
const reference to TLI.

This patch passes them by value which is consistent with the vast
majority of code.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D120420