staging:rtl8192u: Rename RxPktPendingTimer - Style

Rename the member variable RxPktPendingTimer to rx_pkt_pending_timer.
This change clears the checkpatch issue with CamelCase naming.

The resulting changes are coding style changes in nature so 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>