perf tools: Increase maximum number of events in expressions

Some of the upcoming metrics need more than 8 events. Increase the maximum
number the parser supports.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170811232634.30465-9-andi@firstfloor.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/expr.h

 #ifndef PARSE_CTX_H
 #define PARSE_CTX_H 1
 
-#define EXPR_MAX_OTHER 8
+#define EXPR_MAX_OTHER 15
 #define MAX_PARSE_ID EXPR_MAX_OTHER
 
 struct parse_id {