drd: Change VALGRIND_DO_CLIENT_REQUEST_EXPR() into VALGRIND_DO_CLIENT_REQUEST_STMT() where appropriate

This should silence a few clang warnings. This was reported by Florian.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13595 a5019735-40e9-0310-863c-91ae7b9d1cf9