staging:rtl8192u: Rename Register Constants - Style

The four register constants, 'Current_Tx_Rate_Reg',
'Initial_Tx_Rate_Reg', 'Tx_Retry_Count_Reg' and 'RegC38_TH' all cause
checkpatch issue with CamelCase naming. The three have been renamed to
'CURRENT_TX_RATE_REG', 'INITIAL_TX_RATE_REG', 'TX_RETRY_COUNT_REG' and
'REG_C38_TH' respectively.

These are coding style changes 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>