perf top: Don't complain about lack of vmlinux when not resolving some kernel samples

perf top: Don't complain about lack of vmlinux when not resolving some kernel samples

Recently we got a case where a kernel sample wasn't being resolved due
to a bug that was not setting the end address on kernel functions
implemented in assembly (see Link: tag), and then those were not being
found by machine__resolve() -> map__find_symbol().

So we ended up with:

  # perf top --stdio
  PerfTop: 0 irqs/s  kernel: 0%  exact: 0% lost: 0/0 drop: 0/0 [cycles/P]
  -----------------------------------------------------------------------

  Warning:
  A vmlinux file was not found.
  Kernel samples will not be resolved.
  ^Z
  [1]+  Stopped                 perf top --stdio
  #

But then resolving all other kernel symbols.

So just fixup the logic to only print that warning when there are no
symbols in the kernel map.

Fixes: d88205db9caa0e9d ("perf dso: Add dso__has_symbols() method")
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/lkml/Z3buKhcCsZi3_aGb@x1
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>