perf dso: Fix memory leak in dso__new_map()

perf dso: Fix memory leak in dso__new_map()

ASan reports a memory leak when running:

  # perf test "65: maps__merge_in".

The causes of the leaks are two, this patch addresses only the first
one, which is related to dso__new_map().

The bug is that dso__new_map() creates a new dso but never decreases the
refcount it gets from creating it.

This patch adds the missing dso__put().

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Fixes: d3a7c489c7fd2463 ("perf tools: Reference count struct dso")
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/60bfe0cd06e89e2ca33646eb8468d7f5de2ee597.1626343282.git.rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>