perf tools: Increase MAX_EVENT_LENGTH

The name length of some trace events is longer than 30, like
sys_enter_sched_get_priority_max and
ext4_mb_discard_preallocations.

Passing those events to perf-record will fail, try:

  # ./perf record -f -e syscalls:sys_enter_sched_get_priority_max -F 1 -a

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <4AB1F4AB.7050205@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>