AMDGPU: Fix crash when disassembling VOP3 mac

The unused dummy src2_modifiers is missing, so it crashes
when trying to print it.

I tried to fully remove src2_modifiers, but there are some
irritations in the places where it is converted to mad since
it starts to require modifying use lists while iterating over
them.

llvm-svn: 299861
diff --git a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
index ec1d2c3..ca492b9 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
@@ -16,6 +16,7 @@
 
 #include "AMDGPUMachineFunction.h"
 #include "SIRegisterInfo.h"
+#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
 #include "llvm/CodeGen/PseudoSourceValue.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/Support/ErrorHandling.h"