perf debug: Rename __eprintf(va_list args) to veprintf

Adhering to the naming convention used when va_args is in a printf like
function, e.g. stdio.h.

Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-b5l3wt77ct28dcnriguxtvn6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>