No need to check whether unsigned variable is less than 0.

CC: Luciano Coelho <coelho@ti.com>
CC: linux-wireless@vger.kernel.org
CC: netdev@vger.kernel.org
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Luciano Coelho <luca@coelho.fi>