gpio: pca953x: Fix corruption of other gpios in set_multiple.

gpiod_set_array_value_complex does not clear the bits field.
Therefore when the drivers set_multiple funciton is called bits outside
the mask are undefined and can be either set or not. So bank_val needs
to be masked with bank_mask before or with the reg_val cache.

Cc: stable@vger.kernel.org
Fixes: b4818afe

 ("gpio: pca953x: Add set_multiple to allow multiple")
Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>