ARM: dts: exynos: Align SPI GPIO node name with dtschema in Galaxy I9100

The device tree schema expects SPI controller to be named "spi",
otherwise dtbs_check complain with a warning like:

  arch/arm/boot/dts/exynos4210-i9100.dt.yaml: spi-lcd:
    $nodename:0: 'spi-lcd' does not match '^spi(@.*|-[0-9a-f])*$'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200830135200.24304-15-krzk@kernel.org

arch/arm/boot/dts/exynos4210-i9100.dts

@@ -147,7 +147,7 @@ battery@36 {
 		};
 	};
 
-	spi-lcd {
+	spi-3 {
 		compatible = "spi-gpio";
 		#address-cells = <1>;
 		#size-cells = <0>;