USB: serial: keyspan_usa: add proper SPDX lines for .h files

The keyspan_usa??msg.h files are under a BSD-3 style license, so
properly label them as such with a SPDX line at the top of the file.
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/keyspan_usa26msg.h

+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
 	usa26msg.h
 

drivers/usb/serial/keyspan_usa28msg.h

+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
 	usa28msg.h
 

drivers/usb/serial/keyspan_usa49msg.h

+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
 	usa49msg.h
 

drivers/usb/serial/keyspan_usa67msg.h

+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
 	usa67msg.h
 

drivers/usb/serial/keyspan_usa90msg.h

+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
 	usa90msg.h