perf hists: Clarify callchain disabling when available

perf hists: Clarify callchain disabling when available

We want to allow having mixed events with/without callchains, not
using a global flag to show callchains, but allowing supressing
callchains when they are present.

So invert the logic of the last parameter to hists__fprint() to
that effect.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-ohqyisr6qge79qa95ojslptx@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>