gpio: pca953x: Use correct u16 value for register word write

[ Upstream commit 9b8e3ec34318663affced3c14d960e78d760dd9a ]

The current implementation only uses the first byte in val,
the second byte is always 0. Change it to use cpu_to_le16
to write the two bytes into the register

Cc: stable@vger.kernel.org
Signed-off-by: Yong Li <sdliyong@gmail.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>