USB: fix USBTMC get_capabilities success handling

In order:
Add reference to relevant section of USBTMC usb488 subclass specs.
Print debug output of capabilities only when it was retrieved successfully.
Clear return value on success, otherwise driver always reports failure.
Signed-off-by: Gergely Imreh <imrehg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/usbtmc.c

@@ -57,7 +57,9 @@ MODULE_DEVICE_TABLE(usb, usbtmc_devices);
 
 /*
  * This structure is the capabilities for the device
- * See section 4.2.1.8 of the USBTMC specification for details.
+ * See section 4.2.1.8 of the USBTMC specification,
+ * and section 4.2.2 of the USBTMC usb488 subclass
+ * specification for details.
  */
 struct usbtmc_dev_capabilities {
 	__u8 interface_capabilities;
@@ -796,20 +798,21 @@ static int get_capabilities(struct usbtmc_device_data *data)
 	}
 
 	dev_dbg(dev, "GET_CAPABILITIES returned %x\n", buffer[0]);
-	dev_dbg(dev, "Interface capabilities are %x\n", buffer[4]);
-	dev_dbg(dev, "Device capabilities are %x\n", buffer[5]);
-	dev_dbg(dev, "USB488 interface capabilities are %x\n", buffer[14]);
-	dev_dbg(dev, "USB488 device capabilities are %x\n", buffer[15]);
 	if (buffer[0] != USBTMC_STATUS_SUCCESS) {
 		dev_err(dev, "GET_CAPABILITIES returned %x\n", buffer[0]);
 		rv = -EPERM;
 		goto err_out;
 	}
+	dev_dbg(dev, "Interface capabilities are %x\n", buffer[4]);
+	dev_dbg(dev, "Device capabilities are %x\n", buffer[5]);
+	dev_dbg(dev, "USB488 interface capabilities are %x\n", buffer[14]);
+	dev_dbg(dev, "USB488 device capabilities are %x\n", buffer[15]);
 
 	data->capabilities.interface_capabilities = buffer[4];
 	data->capabilities.device_capabilities = buffer[5];
 	data->capabilities.usb488_interface_capabilities = buffer[14];
 	data->capabilities.usb488_device_capabilities = buffer[15];
+	rv = 0;
 
 err_out:
 	kfree(buffer);