perf top: Fix the 'E' hotkey, select among multiple events

We were not recognizing 'E' as a hotkey due to a bug introduced when
switching to the new, hist_entry based top. Fix it by returning that 'E'
is mapped if evlist->nr_entries > 1.
Reported-by: Mike Galbraith <efault@gmx.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-zcx055vnhagddvqlaqxvdhtb@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -438,6 +438,7 @@ static int key_mapped(int c)
 		case 'S':
 			return 1;
 		case 'E':
+			return top.evlist->nr_entries > 1 ? 1 : 0;
 		default:
 			break;
 	}