rtl8187: remove setting of beacon/atim registers from initialization

On 8187B path, we set a initial value for beacon interval and atim
window on initialization. But this isn't needed, since same setup is
done on rtl8187_config.

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>