staging:rtl8192u: Rename CmdID_RF_WriteReg > CMD_ID_RF_WRITE_REG - Style

Rename enum label CmdID_RF_WriteReg to CMD_ID_RF_WRITE_REG. This change clears
the checkpatch issue with CamelCase. The change is style only and should not
impact code execution.

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