perf symbols: Do not check ss->dynsym twice

ss->dynsym is checked to be not NULL twice. Remove the first check
because, in fact, there can be a plt with no dynsym, which is something
that will be dealt with later.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20230120123456.12449-7-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>