perf: xgene: Remove set but not used variable 'config'

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

drivers/perf/xgene_pmu.c: In function 'xgene_perf_stop':
drivers/perf/xgene_pmu.c:1055:6: warning:
 variable 'config' set but not used [-Wunused-but-set-variable]

It never used since introduction.
Signed-off-by: NYue Haibing <yuehaibing@huawei.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

drivers/perf/xgene_pmu.c

@@ -1057,7 +1057,6 @@ static void xgene_perf_start(struct perf_event *event, int flags)
 static void xgene_perf_stop(struct perf_event *event, int flags)
 {
 	struct hw_perf_event *hw = &event->hw;
-	u64 config;
 
 	if (hw->state & PERF_HES_UPTODATE)
 		return;
@@ -1069,7 +1068,6 @@ static void xgene_perf_stop(struct perf_event *event, int flags)
 	if (hw->state & PERF_HES_UPTODATE)
 		return;
 
-	config = hw->config;
 	xgene_perf_read(event);
 	hw->state |= PERF_HES_UPTODATE;
 }