sh: perf events: Fix up uninitialized variable warning.

'config' can be unintialized, and although it's not really an error, it
still manages to trigger the -Werror with certain toolchains. Initialize
it early to shut up gcc.

Signed-off-by: Paul Mundt <[e-mail]>

arch/sh/kernel/perf_event.c

···
 {
 	struct perf_event_attr *attr = &event->attr;
 	struct hw_perf_event *hwc = &event->hw;
-	int config;
+	int config = -1;
 	int err;
 
 	if (!sh_pmu_initialized())
···
 
 		config = sh_pmu->event_map(attr->config);
 		break;
-	default:
-		return -EINVAL;
 	}
 
 	if (config == -1)