[X86] Fix the bug of pr62625

We should not call tryOptimizeLEAtoMOV() in eliminateFrameIndex() when
the base register is a virtual register, because tryOptimizeLEAtoMOV
would assume the base register be physical register. Although we can
also optimize LEA to MOV with virtual register, I'd like to leave the
optimization in another patch.

Differential Revision: https://reviews.llvm.org/D150521