perf symbols: Add missing dso.h header

This was being obtained only indirectly, by luck.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-xeolxwr3iftwfw9kmw26shfe@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -7,6 +7,7 @@
 #include <unistd.h>
 #include <inttypes.h>
 
+#include "dso.h"
 #include "map.h"
 #include "map_groups.h"
 #include "symbol.h"