app/eventdev: fix build with gcc 4.8

app/eventdev: fix build with gcc 4.8

test_perf_common.c: In function ‘perf_event_timer_producer’:
test_perf_common.c:99:3: error: missing initializer for
 field ‘priority’ of ‘struct <anonymous>’
 [-Werror=missing-field-initializers]
   .ev.sched_type = t->opt->sched_type_list[0],

Fixes: d008f20bce23 ("app/eventdev: add event timer adapter as a producer")

Reported-by: Andrew Rybchenko <arybchenko@solarflare.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
Tested-by: Andrew Rybchenko <arybchenko@solarflare.com>