Use a reference instead of a pointer.

This makes using a std::unique_ptr in the caller more convenient.

llvm-svn: 214433
diff --git a/llvm/lib/DebugInfo/DIContext.cpp b/llvm/lib/DebugInfo/DIContext.cpp
index 49a4409..29ef8f2 100644
--- a/llvm/lib/DebugInfo/DIContext.cpp
+++ b/llvm/lib/DebugInfo/DIContext.cpp
@@ -13,6 +13,6 @@
 
 DIContext::~DIContext() {}
 
-DIContext *DIContext::getDWARFContext(object::ObjectFile *Obj) {
+DIContext *DIContext::getDWARFContext(object::ObjectFile &Obj) {
   return new DWARFContextInMemory(Obj);
 }