Add a missing def flag.

*** Bad machine code: Explicit definition marked as use ***
- function:    test_cos
- basic block: BB#0 L.entry (0x7ff2a2024fd0)
- instruction: VSETLNi32 %D11, %D11<undef>, %R0, 0, pred:14, pred:%noreg, %Q5<imp-use,kill>, %Q5<imp-def>
- operand 0:   %D11

llvm-svn: 162247