ARM: dts: imx6qdl-tqma6: fix LM75 compatible string

Specify the National LM75 sensor including its vendor name, as mandated
by the binding docs.

Fixes: cac849e9bbc8 ("ARM: dts: imx6qdl: add TQMa6{S,Q,QP} SoM")
Signed-off-by: Matthias Schiffer <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6qdl-tqma6a.dtsi

···
 	};
 
 	sensor@48 {
-		compatible = "lm75";
+		compatible = "national,lm75";
 		reg = <0x48>;
 	};
 

arch/arm/boot/dts/imx6qdl-tqma6b.dtsi

···
 	};
 
 	sensor@48 {
-		compatible = "lm75";
+		compatible = "national,lm75";
 		reg = <0x48>;
 	};