ARM: davinci: fix the GPIO lookup for omapl138-hawk

The GPIO chip is called davinci_gpio.0 in legacy mode. Fix it, so that
mmc can correctly lookup the wp and cp gpios.

Note that it is the gpio-davinci driver that sets the gpiochip label to
davinci_gpio.0.

Fixes: c69f43fb ("ARM: davinci: hawk: use gpio descriptor for mmc pins")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
[nsekhar@ti.com: add a note on where the chip label is set]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>