rtl8187: consolidate anaparam on/off write sequences

There are repeated calls for anaparam on/off sequence in the code.
Consolidate the common code in rtl8187_set_anaparam and use it where
needed.

Signed-off-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>