[LLD] [COFF] Update a leftover comment after SVN r374869. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@374874 91177308-0d34-0410-b5e6-96231b3b80d8

COFF/PDB.cpp

@@ -1789,7 +1789,7 @@ static bool findLineTable(const SectionChunk *c, uint32_t addr,
 }
 
 // Use CodeView line tables to resolve a file and line number for the given
-// offset into the given chunk and return them, or {"", 0} if a line table was
+// offset into the given chunk and return them, or None if a line table was
 // not found.
 Optional<std::pair<StringRef, uint32_t>>
 getFileLineCodeView(const SectionChunk *c, uint32_t addr) {