ptp: Don't print an error if ptp_kvm is not supported

Commit 300bb1f ("ptp: arm/arm64: Enable ptp_kvm for arm/arm64")
enable ptp_kvm support for ARM platforms and for any ARM platform that
does not support this, the following error message is displayed ...

 ERR KERN fail to initialize ptp_kvm

For platforms that do not support ptp_kvm this error is a bit misleading
and so fix this by only printing this message if the error returned by
kvm_arch_ptp_init() is not -EOPNOTSUPP. Note that -EOPNOTSUPP is only
returned by ARM platforms today if ptp_kvm is not supported.

Fixes: 300bb1f ("ptp: arm/arm64: Enable ptp_kvm for arm/arm64")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210420132419.1318148-1-jonathanh@nvidia.com

drivers/ptp/ptp_kvm_common.c

@@ -138,7 +138,8 @@ static int __init ptp_kvm_init(void)
 
 	ret = kvm_arch_ptp_init();
 	if (ret) {
-		pr_err("fail to initialize ptp_kvm");
+		if (ret != -EOPNOTSUPP)
+			pr_err("fail to initialize ptp_kvm");
 		return ret;
 	}