perf hists: Rename hist_entry__add_pair arguments

perf hists: Rename hist_entry__add_pair arguments

The current logic is to attach pair to the leader hist_entry.

Arguments of hist_entry__add_pair function were placed the other way
round.. driving me crazy.

I.e. list_add_tail expects (new_node, head).

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1355404152-16523-3-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>