pinctrl: bcm281xx: Add missing assignment in bcm21664_pinctrl_lock_all()

pinctrl: bcm281xx: Add missing assignment in bcm21664_pinctrl_lock_all()

The next line checks if this regmap_write() failed, but it doesn't
work because the assignment was accidentally left out.  Add the
assignment.

Fixes: 60d69769c851 ("pinctrl: bcm281xx: Add support for BCM21664 pinmux")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Artur Weber <aweber.kernel@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/dfc15d59-7fa9-4f96-aacb-37c3df6d420d@stanley.mountain
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>