gpio: pca953x: Fix pca953x_gpio_set_multiple() on 64-bit

pca953x_gpio_set_multiple() divides by 4 to convert from longs to bytes,
which assumes a 32-bit platform, and is not correct on 64-bit platforms.
Use "sizeof(...)" instead to fix this.

Cc: stable@vger.kernel.org
Fixes: b4818afe ("gpio: pca953x: Add set_multiple to allow multiple bits to be set in one write.")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>