cxl: Fix PSL timebase synchronization detection

The PSL timebase synchronization is seemingly failing for
configuration not including VIRT_CPU_ACCOUNTING_NATIVE. The driver
shows the following trace in dmesg:
PSL: Timebase sync: giving up!

The PSL timebase register is actually syncing correctly, but the cxl
driver is not detecting it. Fix is to use the proper timebase-to-time
conversion.
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org> # 4.3+
Acked-by: Michael Neuling <mikey@neuling.org>
Reviewed-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/pci.c

@@ -415,7 +415,7 @@ static int cxl_setup_psl_timebase(struct cxl *adapter, struct pci_dev *dev)
 		delta = mftb() - psl_tb;
 		if (delta < 0)
 			delta = -delta;
-	} while (cputime_to_usecs(delta) > 16);
+	} while (tb_to_ns(delta) > 16000);
 
 	return 0;
 }