perf map: Turn some pr_warning() to pr_debug()

Annoying when using it with --stdio/--stdio2, so just turn them debug,
we can get those using -v.

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-t3684lkugnf1w4lwcmpj9ivm@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>