arm: mvebu: Fix pinctrl for Armada 370 Mirabox SDIO port.

The previous configuration used the wrong "clk" pin.  Without this
change mv_sdio worked because the bootloader would set the pin up, but
with a bootloader that does not set the pin, mv_sdio fails to detect any
card.

I have tested this change using a mwifiex_sdio wireless network adapter
over the SDIO interface.
Signed-off-by: Ryan Press <ryan@presslab.us>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

arch/arm/boot/dts/armada-370-mirabox.dts

@@ -54,7 +54,7 @@ ethernet@d0074000 {
 		};
 
 		mvsdio@d00d4000 {
-			pinctrl-0 = <&sdio_pins2>;
+			pinctrl-0 = <&sdio_pins3>;
 			pinctrl-names = "default";
 			status = "okay";
 			/*

arch/arm/boot/dts/armada-370.dtsi

@@ -59,6 +59,12 @@ sdio_pins2: sdio-pins2 {
 					     "mpp50", "mpp51", "mpp52";
 			      marvell,function = "sd0";
 			};
+
+			sdio_pins3: sdio-pins3 {
+			      marvell,pins = "mpp48", "mpp49", "mpp50",
+					     "mpp51", "mpp52", "mpp53";
+			      marvell,function = "sd0";
+			};
 	        };
 
 		gpio0: gpio@d0018100 {