KVM: PPC: Book3S HV: Return ENODEV error rather than EIO

If an attempt is made to load the kvm-hv module on a machine which
doesn't have hypervisor mode available, return an ENODEV error,
which is the conventional thing to return to indicate that this
module is not applicable to the hardware of the current machine,
rather than EIO, which causes a warning to be printed.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Scott Wood <scottwood@freescale.com>