[Clang] [NFC] Fix trailing whitespace in Parser.h (llvm#165498)

Many editors and IDEs automatically delete trailing whitespace on save,
and this particular one has shown up as an unrelated change in several
of my patches that I then had to remove later (and I’ve seen it in other
people’s patches too); this has wasted too much of my time, so I’m
removing it separately.

Author: Sirraide

clang/include/clang/Parse/Parser.h

@@ -7677,7 +7677,7 @@ class Parser : public CodeCompletionHandler {
   /// [GNU] asm-clobbers:
   ///         asm-string-literal
   ///         asm-clobbers ',' asm-string-literal
-  /// \endverbatim 
+  /// \endverbatim
   ///
   StmtResult ParseAsmStatement(bool &msAsm);