perf tools: Rename global variable 'events' in util/header.c

Trivial patch that renames global variable 'events' in util/header.c.

Use a more specific naming to avoid conflicts. Same for variable
'event_count'.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1345144224-27280-5-git-send-email-robert.richter@amd.com


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