ipmi: Use defined constant for UUID representation

Instead of magic number use pre-defined constant for UUID binary and
string representations.

While here, drop the implementation details of guid_t type.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[Also converted a "17" in the error string to UUID_SIZE + 1]
Signed-off-by: Corey Minyard <cminyard@mvista.com>

drivers/char/ipmi/ipmi_msghandler.c

@@ -2749,7 +2749,7 @@ static ssize_t guid_show(struct device *dev, struct device_attribute *attr,
 	if (!guid_set)
 		return -ENOENT;
 
-	return snprintf(buf, 38, "%pUl\n", guid.b);
+	return snprintf(buf, UUID_STRING_LEN + 1 + 1, "%pUl\n", &guid);
 }
 static DEVICE_ATTR_RO(guid);
 
@@ -3148,11 +3148,11 @@ static void guid_handler(struct ipmi_smi *intf, struct ipmi_recv_msg *msg)
 		goto out;
 	}
 
-	if (msg->msg.data_len < 17) {
+	if (msg->msg.data_len < UUID_SIZE + 1) {
 		bmc->dyn_guid_set = 0;
 		dev_warn(intf->si_dev,
-			 "The GUID response from the BMC was too short, it was %d but should have been 17.  Assuming GUID is not available.\n",
-			 msg->msg.data_len);
+			 "The GUID response from the BMC was too short, it was %d but should have been %d.  Assuming GUID is not available.\n",
+			 msg->msg.data_len, UUID_SIZE + 1);
 		goto out;
 	}