arm: pmu: Improve PMU error reporting

The KVM ioctls mostly just return -1 in the error case, leaving the
actual error code in errno.

Change the output of the PMU error message to actually print this error
code instead of the generic -1.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arm/pmu.c

@@ -18,7 +18,7 @@ static int set_pmu_attr(struct kvm *kvm, int vcpu_idx,
 	if (!ret) {
 		ret = ioctl(fd, KVM_SET_DEVICE_ATTR, attr);
 		if (ret)
-			pr_err("PMU KVM_SET_DEVICE_ATTR failed (%d)\n", ret);
+			perror("PMU KVM_SET_DEVICE_ATTR failed");
 	} else {
 		pr_err("Unsupported PMU on vcpu%d\n", vcpu_idx);
 	}