pinctrl: bcm: Simplify bool comparison

Fix the follow coccicheck warnings:

./drivers/pinctrl/bcm/pinctrl-ns2-mux.c:856:29-38: WARNING:
Comparison to bool.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Link: https://lore.kernel.org/r/1610705349-24310-1-git-send-email-abaci-bugfix@linux.alibaba.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>