R600/SI: Fix assertion from copying a TargetGlobalAddress

R600/SI: Fix assertion from copying a TargetGlobalAddress

Assert in scheduler from an inserted copy_to_regclass from
a constant.

This only seems to break sometimes when a constant initializer
address is forced into VGPRs in a non-entry block. No test
since the only case I've managed to hit only happens with a future
patch, and that case will also not be a problem once scalar instructions
are used in non-entry blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217380 91177308-0d34-0410-b5e6-96231b3b80d8