[PowerPC] Fix conditions of assert in PPCAsmPrinter

Summary:
g++ build emits warning:

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp:667:77: error: suggest parentheses around ?&&? within ?||? [-Werror=parentheses]
     assert(MO.isGlobal() || MO.isCPI() || MO.isJTI() || MO.isBlockAddress() &&
                                                         ~~~~~~~~~~~~~~~~~~~~^~
            "Unexpected operand type for LWZtoc pseudo.");

I believe the intension is to assert all different types,
so we should add a parentheses to include all '||'.

Reviewers: #powerpc, sfertile, hubert.reinterpretcast, Xiangling_L

Reviewed By: Xiangling_L

Subscribers: wuzish, nemanjai, hiraditya, kbarton, MaskRay, shchenz, steven.zhang, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68180

llvm-svn: 373164