perf scripts python: call-graph-from-sql.py: Change icon

There are not many standard icons, but the computer icon looks slightly
better than the information icon.

Committer testing:

Noticed the change on the icon on the gnome menu right next to the
"Activities" menu, looks nicer indeed.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20181001062853.28285-5-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>