staging:rtl8192u: Rename TxCurSeq - Style

Rename the member variable TxCurSeq to tx_cur_seq. This change clears
the checkpatch issue with CamelCase naming.

The changes are coding style changes which should not impact runtime
code execution.

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