[DebugInfo] Don't insert DEBUG_VALUE after terminators

r314974 introduced insertion of DEBUG_VALUEs after
each redefinition of debug value register in the slot index range.

In case the instruction redefining the debug value register
was a terminator, machine verifier would complain since it
enforces the rule of no non-terminator instructions
following the first terminator.

Differential Revision: https://reviews.llvm.org/D42801

llvm-svn: 324734