perf evsel: Introduce perf_evsel__prev() method

Just one use so far, on the hists browser, for completeness since there
we use perf_evlist__{first,last} and perf_evsel__next() for handling the
TAB and UNTAB keys.

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/ui/browsers/hists.c

···
 				if (pos->node.prev == &evlist->entries)
 					pos = perf_evlist__last(evlist);
 				else
-					pos = list_entry(pos->node.prev, struct perf_evsel, node);
+					pos = perf_evsel__prev(pos);
 				goto browse_hists;
 			case K_ESC:
 				if (!ui_browser__dialog_yesno(&menu->b,

tools/perf/util/evsel.h

···
 	return list_entry(evsel->node.next, struct perf_evsel, node);
 }
 
+static inline struct perf_evsel *perf_evsel__prev(struct perf_evsel *evsel)
+{
+	return list_entry(evsel->node.prev, struct perf_evsel, node);
+}
+
 /**
  * perf_evsel__is_group_leader - Return whether given evsel is a leader event
  *