pinctrl: bcm2835: Replace BUG with BUG_ON

The if condition followed by BUG can be replaced to BUG_ON which is
more compact and formal in linux source.

Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210624064913.41788-1-wangborong@cdjrlc.com


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