USB: atm: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in header file related to USB DSL modem support drivers. For C header files Documentation/process/license-rules.rst mandates C-like comments (opposed to C source files where C++ style should be used).

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46.

---
 drivers/usb/atm/usbatm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8725755bd53d..d96658e2e209 100644
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /******************************************************************************
  *  usbatm.h - Generic USB xDSL driver core
  *

2.17.1