char: ipmi: eliminate misleading print info when being probed via ACPI

When ipmi is probed via ACPI, the boot log shows

[   17.945139] ipmi_si IPI0001:00: probing via device tree
[   17.950369] ipmi_si IPI0001:00: ipmi_si: probing via ACPI
[   17.955795] ipmi_si IPI0001:00: [io  0x00e4-0x3fff] regsize 1 spacing 1 irq 0
[   17.962932] ipmi_si: Adding ACPI-specified bt state machine

which "ipmi_si IPI0001:00: probing via device tree" is misleading
with a ACPI HID "IPI0001" but probing via DT.

Eliminate this misleading print info by checking of_node is valid
or not before calling of_ipmi_probe().
Signed-off-by: NHanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: NCorey Minyard <cminyard@mvista.com>

drivers/char/ipmi/ipmi_si_intf.c

@@ -2784,7 +2784,7 @@ static int acpi_ipmi_probe(struct platform_device *dev)
 
 static int ipmi_probe(struct platform_device *dev)
 {
-	if (of_ipmi_probe(dev) == 0)
+	if (dev->dev.of_node && of_ipmi_probe(dev) == 0)
 		return 0;
 
 	if (acpi_ipmi_probe(dev) == 0)