MCDwarf.h: Prune a few stray \param(s). [-Wdocumentation]

\param should be used to describe individual parameters. Use a command like \a or \c for visual enhancements.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189905 91177308-0d34-0410-b5e6-96231b3b80d8