[TTI] Change new getVectorInstrCost overload to use const reference after D131114

[TTI] Change new getVectorInstrCost overload to use const reference after D131114

A const reference is preferred over a non-null const pointer.
`Type *` is kept as is to match the other overload.

Reviewed By: davidxl

Differential Revision: https://reviews.llvm.org/D131197