staging: rtl8192u: add proper SPDX identifiers on files that did not have them.

There were a few files for the rtl8192u driver that did not have SPDX
identifiers on them, so fix that up.  At the same time, remove the "free
form" text that specified the license of the file, as that is impossible
for any tool to properly parse.

Cc: John Whitmore <johnfwhitmore@gmail.com>
Cc: Bhanusree Pola <bhanusreemahesh@gmail.com>
Cc: Sanjana Sanikommu <sanjana99reddy99@gmail.com>
Cc: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>