b43: phy_ht: Remove 9 year old TODO

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/broadcom/b43/phy_ht.c: In function ‘b43_phy_ht_op_init’:
 drivers/net/wireless/broadcom/b43/phy_ht.c:904:3: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]

Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "Alexander A. Klimov" <grandmaster@al2klimov.de>
Cc: linux-wireless@vger.kernel.org
Cc: b43-dev@lists.infradead.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200821071644.109970-18-lee.jones@linaro.org