pinctrl-sx150x: Remove excessive locking

Gpiochip and irqchip aspects of this driver do not access any shared
registers on the chip itself and atomicity of various regmap operations
is ensured by that API's implementation, so there doesn't seem to be a
reason to hold the lock in as many places as it is held now.

Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>