staging: wilc1000: rename enum CURRENT_TXRATE to use lowercase

Cleanup patch to rename enums in lowercase to follow linux coding style.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>