powerpc/perf: Remove set but not used variable 'target'

Fix gcc '-Wunused-but-set-variable' warning:

arch/powerpc/perf/imc-pmu.c: In function trace_imc_event_init:
arch/powerpc/perf/imc-pmu.c:1292:22: warning: variable target set but not used [-Wunused-but-set-variable]

It is introduced by commit 012ae244 ("powerpc/perf:
Trace imc PMU functions"), but never used, so remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1574144074-142032-3-git-send-email-zhengbin13@huawei.com

arch/powerpc/perf/imc-pmu.c

@@ -1426,8 +1426,6 @@ static void trace_imc_event_del(struct perf_event *event, int flags)
 
 static int trace_imc_event_init(struct perf_event *event)
 {
-	struct task_struct *target;
-
 	if (event->attr.type != event->pmu->type)
 		return -ENOENT;
 
@@ -1458,7 +1456,6 @@ static int trace_imc_event_init(struct perf_event *event)
 	mutex_unlock(&imc_global_refc.lock);
 
 	event->hw.idx = -1;
-	target = event->hw.target;
 
 	event->pmu->task_ctx_nr = perf_hw_context;
 	event->destroy = reset_global_refc;