[SLP] Fix PR35047: Fix default cost model for cast op in X86.

Summary:
The cost calculation for default case on X86 target does not always
follow correct wayt because of missing 4-th argument in
`BaseT::getCastInstrCost()` call. Added this missing parameter.

Reviewers: hfinkel, mkuper, RKSimon, spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39687

llvm-svn: 317576