[llvm-exegesis] deserializeMCInst(): bump SmallVector small size up to 16

Summary:
... from 8.
`VALIGNDZ128rmbik XMM0 XMM0 K1 XMM3 RDI i_0x1  i_0x0  i_0x1` instruction already has 9 components.
It does not matter much in terms of performance, but avoiding allocation seems to come with low cost here..

Reviewers: courbet, gchatelet

Reviewed By: courbet

Subscribers: tschuett, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57654

llvm-svn: 353022