ARM: dts: imx25-pinfunc: Fix gpio function name for pads GPIO_[A-F]

The pinfunc definitions used GPIO_A as function instead of GPIO_1_0 as
done for all the other pins with GPIO functionality. Fix for consistency.

There are no mainline users that needs adaption.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>