staging:rtl8192u: Rename CmdID - Style

Rename the member variable CmdId to cmd_id. This change clears the
checkpatch issue with CamelCase naming. The change is purely a coding
style change which should have no impact on runtime code execution.

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