staging: rtl8192e: Add SPDX-License-Identifier - Style

Add SPDX-Licens-Identifier tag to the start of the file. This is
a coding style change which should not impact the runtime code execution.

Signed-off-by: Zach Turner <turnerzdp@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>