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

 drivers/net/wireless/cisco/airo.c: In function ‘airo_init_module’:
 drivers/net/wireless/cisco/airo.c:5663:21: 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: Benjamin Reed <breed@users.sourceforge.net>
Cc: Javier Achirica <achirica@users.sourceforge.net>
Cc: Jean Tourrilhes <jt@hpl.hp.com>
Cc: Fabrice Bellet <fabrice@bellet.info>
Cc: linux-wireless@vger.kernel.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/20200814113933.1903438-12-lee.jones@linaro.org