gpio: pca953x: enfore type for i2c_smbus_write_word_data()

The commit 9b8e3ec3 ("gpio: pca953x: Use correct u16 value for register
word write") fixed regression in pca953x_write_regs(). At the same time the
solution introduced a sparse warning:

drivers/gpio/gpio-pca953x.c:168:39: warning: incorrect type in argument 3 (different base types)
drivers/gpio/gpio-pca953x.c:168:39:    expected unsigned short [unsigned] [usertype] value
drivers/gpio/gpio-pca953x.c:168:39:    got restricted __le16 [usertype] <noident>

Fix the code by enforcing the type of i2c_smbus_write_word_data() parameter.

Cc: Yong Li <sdliyong@gmail.com>
Cc: Phil Reid <preid@electromag.com.au>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>