staging:rtl8192u: Rename SwChnlCmdID > switch_chan_cmd_id - Coding Style

Rename enumerated type to clear a CamelCase warning from checkpatch. The
change is style only. No impact on run time execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>