Use SmallVectorImpl& instead of SmallVector to avoid repeating small vector size.

llvm-svn: 186274
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 757f60b..dacdbdd 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -394,7 +394,7 @@
 /// collectDebgValues - Scan instructions following MI and collect any
 /// matching DBG_VALUEs.
 static void collectDebugValues(MachineInstr *MI,
-                               SmallVector<MachineInstr *, 2> & DbgValues) {
+                               SmallVectorImpl<MachineInstr *> &DbgValues) {
   DbgValues.clear();
   if (!MI->getOperand(0).isReg())
     return;