arm-cci: don't return value from void function

pmu_write_register has a void return type, so remove the useless return
statement.
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/bus/arm-cci.c

@@ -758,7 +758,7 @@ static u32 pmu_read_register(struct cci_pmu *cci_pmu, int idx, unsigned int offs
 static void pmu_write_register(struct cci_pmu *cci_pmu, u32 value,
 			       int idx, unsigned int offset)
 {
-	return writel_relaxed(value, cci_pmu->base +
+	writel_relaxed(value, cci_pmu->base +
 		       CCI_PMU_CNTR_BASE(cci_pmu->model, idx) + offset);
 }