staging:rtl8192u: Rename MaxTxPwrDbmList > max_tx_pwr_dbm_list - Style

Rename the member variable MaxTxPwrDbmList to max_tx_pwr_dbm_list. This
change clears the checkpatch issue with CamelCase naming. The change is
a simple coding style change which should not impact runtime code execution.

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