perf tools: No need to check if the argument to __get() function is NULL

Those functions always check if the argument is NULL before trying to
grab a reference count, and also will return the received object, so, to
make code more compact, no need to check for NULL.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-i9wycjdxh0fwhryu55lmafks@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/hist.c

@@ -1039,7 +1039,7 @@ int hist_entry_iter__add(struct hist_entry_iter *iter, struct addr_location *al,
 	int err, err2;
 	struct map *alm = NULL;
 
-	if (al && al->map)
+	if (al)
 		alm = map__get(al->map);
 
 	err = sample__resolve_callchain(iter->sample, &callchain_cursor, &iter->parent,