[DWARFLinker] Fix typo and improve comments (NFC)

Fix a typo and improve comments to match the LLVM coding style.

llvm/include/llvm/DWARFLinker/DWARFLinker.h

@@ -205,22 +205,25 @@ class DwarfEmitter {
 
 using UnitListTy = std::vector<std::unique_ptr<CompileUnit>>;
 
-/// this class represents DWARF information for source file
-/// and it`s address map.
+/// This class represents DWARF information for source file
+/// and its address map.
 class DWARFFile {
 public:
   DWARFFile(StringRef Name, DWARFContext *Dwarf, AddressesMap *Addresses,
             const std::vector<std::string> &Warnings)
       : FileName(Name), Dwarf(Dwarf), Addresses(Addresses), Warnings(Warnings) {
   }
 
-  /// object file name.
+  /// The object file name.
   StringRef FileName;
-  /// source DWARF information.
+
+  /// The source DWARF information.
   DWARFContext *Dwarf = nullptr;
-  /// helpful address information(list of valid address ranges, relocations).
+
+  /// Helpful address information(list of valid address ranges, relocations).
   AddressesMap *Addresses = nullptr;
-  /// warnings for object file.
+
+  /// Warnings for this object file.
   const std::vector<std::string> &Warnings;
 };