usbip: fix NULL pointer dereference on errors

Fix NULL pointer dereference and obsolete comments forgotten when
usbip server was converted from an interface driver to a device driver.

Signed-off-by: Alexander Popov <alpopov@ptsecurity.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/usbip/stub_tx.c b/drivers/usb/usbip/stub_tx.c
index dbcabc9..af1edad 100644
--- a/drivers/usb/usbip/stub_tx.c
+++ b/drivers/usb/usbip/stub_tx.c
@@ -229,7 +229,7 @@
 			}
 
 			if (txsize != sizeof(pdu_header) + urb->actual_length) {
-				dev_err(&sdev->interface->dev,
+				dev_err(&sdev->udev->dev,
 					"actual length of urb %d does not match iso packet sizes %zu\n",
 					urb->actual_length,
 					txsize-sizeof(pdu_header));
@@ -261,7 +261,7 @@
 		ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg,
 						iov,  iovnum, txsize);
 		if (ret != txsize) {
-			dev_err(&sdev->interface->dev,
+			dev_err(&sdev->udev->dev,
 				"sendmsg failed!, retval %d for %zd\n",
 				ret, txsize);
 			kfree(iov);
@@ -336,7 +336,7 @@
 		ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg, iov,
 				     1, txsize);
 		if (ret != txsize) {
-			dev_err(&sdev->interface->dev,
+			dev_err(&sdev->udev->dev,
 				"sendmsg failed!, retval %d for %zd\n",
 				ret, txsize);
 			usbip_event_add(&sdev->ud, SDEV_EVENT_ERROR_TCP);