WebGLPrograms: Simplify `getChannel` (#25972)

* WebGLPrograms: Simplify `getChannel`

* Update WebGLPrograms.js

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Co-authored-by: Michael Herzog <[email protected]>

src/renderers/webgl/WebGLPrograms.js

@@ -37,11 +37,9 @@ function WebGLPrograms( renderer, cubemaps, cubeuvmaps, extensions, capabilities
 
 	function getChannel( value ) {
 
-		if ( value === 1 ) return 'uv1';
-		if ( value === 2 ) return 'uv2';
-		if ( value === 3 ) return 'uv3';
+		if ( value === 0 ) return 'uv';
 
-		return 'uv';
+		return `uv${ value }`;
 
 	}