gpio: name PCA953x gpio chips after device name

Instead of using the name directly from the I2C client
to name the gpio_chip, use dev_name() on the client->dev,
so we get the sometimes more unique device name, as I2C has
a mechanism for naming its devices explicitly in e.g.
board data.

This is a prerequisite for being able to reference
uniquely any I2C GPIO expander defined in a board file
when setting up GPIO descriptor tables.

Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>