phy: rockchip-emmc: fix compile issue on arm64 platform

This patch rename "reg" property to "reg_offset".
We rename it to fix the compile issue on ARM64 platform:
(reg_format): "reg" property in /phy has invalid length (4 bytes)
(#address-cells == 2, #size-cells == 2)

This's because "reg" is very special one which should keep the
*-cells with its parent node and can't be overwrited even if we
do that explicitly. On 32-bit plafform, the default *-cells
fit for what we assign to "reg". But that's not correct for 64-bit
platform. So we can see two possible solutions to fix this problem:
A) make phy-rockchip-emmc as a child phy node and overwrite its
parent's #address-cells and #size-cells.
B) avoid using this special property.

we use it just for passing on a offset for different Socs, and there's
no requirement to change the code to make phy-rockchip-emmc as a child
node. so choose option B) is sane.

Change-Id: Ib6a10cb8c3629ec3983854f1bfb7c2426edf79d2
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>

Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt

@@ -6,7 +6,7 @@ Required properties:
  - rockchip,grf : phandle to the syscon managing the "general
    register files"
  - #phy-cells: must be 0
- - reg: PHY configure reg address offset in "general
+ - reg-offset: PHY configure reg address offset in "general
    register files"
 
 Example:
@@ -14,6 +14,6 @@ Example:
 emmcphy: phy {
 	compatible = "rockchip,rk3399-emmc-phy";
 	rockchip,grf = <&grf>;
-	reg = <0xf780>;
+	reg-offset = <0xf780>;
 	#phy-cells = <0>;
 };

drivers/phy/phy-rockchip-emmc.c

@@ -186,7 +186,7 @@ static int rockchip_emmc_phy_probe(struct platform_device *pdev)
 	if (!rk_phy)
 		return -ENOMEM;
 
-	if (of_property_read_u32(dev->of_node, "reg", &reg_offset)) {
+	if (of_property_read_u32(dev->of_node, "reg-offset", &reg_offset)) {
 		dev_err(dev, "missing reg property in node %s\n",
 			dev->of_node->name);
 		return -EINVAL;