staging:rtl8192u: Rename PHY_SetRF8256CCKTxPower() - Style

Rename the function PHY_SetRF8256CCKTxPower() to
phy_set_rf8256_cck_tx_power(), to clear the checkpatch issue with
CamelCase naming.

This is a purely coding style change 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>