Compatible string 'gpio-key' is not existed. Correct it to 'gpio-keys'.

Fix below CHECK_DTBS warnings
arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-ff-rdk-emmc.dtb: /gpio-keys: failed to match any schema with compatible: ['gpio-key']

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
 arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-peb-eval-01.dtsi | 2 +-
 arch/arm/boot/dts/nxp/imx/imx6ull-phytec-tauri.dtsi            | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-peb-eval-01.dtsi b/arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-peb-eval-01.dtsi
index d4d6ce9756390d6b7aa296eb585fc7fe61a67443..24c48cdd1797e43fb364ce6680b4f09bb526e788 100644
--- a/arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-peb-eval-01.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx6ul-phytec-segin-peb-eval-01.dtsi
@@ -8,7 +8,7 @@
 
 / {
 	gpio_keys: gpio-keys {
-		compatible = "gpio-key";
+		compatible = "gpio-keys";
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_gpio_keys>;
 		status = "disabled";
diff --git a/arch/arm/boot/dts/nxp/imx/imx6ull-phytec-tauri.dtsi b/arch/arm/boot/dts/nxp/imx/imx6ull-phytec-tauri.dtsi
index d12fb44aeb140cfacf05a5b257d2106c79392279..8ad09fd334f74cf7e1711a57885564eb9a549902 100644
--- a/arch/arm/boot/dts/nxp/imx/imx6ull-phytec-tauri.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx6ull-phytec-tauri.dtsi
@@ -15,7 +15,7 @@ aliases {
 	};
 
 	gpio_keys: gpio-keys {
-		compatible = "gpio-key";
+		compatible = "gpio-keys";
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_gpio_keys>;
 

-- 
2.34.1