ARM: dts: s5pv210: Correct gpi pinctrl node name

The node name was gpgi, but the pinctrl driver was registering the pins
as just gpi and the "samsung,pins" i2s0 pinctrl entries refer to gpi.
The public S5PC110 datasheet also refers to these pins as just gpi,
so let's make sure everything is in sync and rename the node to gpi.

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>