ARM: dts: imx6sll-evk: correct lcd regulator GPIO pin

On i.MX6SLL EVK board, lcd regulator is controlled
by GPIO4 IO03 using MX6SLL_PAD_KEY_ROW5__GPIO4_IO03 pin,
NOT MX6SLL_PAD_ECSPI1_SCLK__GPIO4_IO08, correct it.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>