staging:rtl8192u: Rename bValid - Style

Rename the member variable bValid to valid, this clears the checkpatch
issue with CamelCase naming.

This is a coding style change which should have no impatch on runtime
code execution.

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