refact: Reuse existing variable

Co-authored-by: Nico Hoffmann  ෴. <me@nhoffmann.com>

Author: bastianallgeier

panel/src/components/Forms/Input/TextareaInput.vue

@@ -173,7 +173,7 @@ export default {
 			const current = input.value;
 
 			if (typeof text === "function") {
-				text = text(this.$refs.input, this.selection());
+				text = text(input, this.selection());
 			}
 
 			this.focus();