Fix typo in syswrap ppoll param, equate ppoll and poll for memcheck testcase.

ppoll argument is called ufds like the poll argument.
Newer architectures (aarch64) implement poll by calling ppoll directly.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14370 a5019735-40e9-0310-863c-91ae7b9d1cf9