rtl8187: Change TX power settings

The latest vendor driver (rtl8187B_linux_26.1036.0708.2008) has a different
CCK power setting code as compared with the Linux driver.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Piter Punk <piterpk@terra.com.br>
Signed-off-by: John W. Linville <linville@tuxdriver.com>