staging:rtl8192u: rename CmdID_SetTxPowerLevel > CMD_ID_SET_TX_PWR_LEVEL

Rename enumeration label CmdID_SetTxPowerLevel to
CMD_ID_SET_TX_PWR_LEVEL. This change clears a checkpatch warning on
CamelCase. The change should not impact runtime execution, style change only.

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