[hyperv] Do not fail if guest OS ID MSR is already set

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/drivers/hyperv/hyperv.c

 	/* Report guest OS identity */
 	guest_os_id = rdmsr ( HV_X64_MSR_GUEST_OS_ID );
 	if ( guest_os_id != 0 ) {
-		DBGC ( hv, "HV %p guest OS ID MSR already set to %#08llx\n",
+		DBGC ( hv, "HV %p guest OS ID MSR was %#08llx\n",
 		       hv, guest_os_id );
-		return -EBUSY;
 	}
 	guest_os_id = HV_GUEST_OS_ID_IPXE;
 	DBGC2 ( hv, "HV %p guest OS ID MSR is %#08llx\n", hv, guest_os_id );