FIR: Minor. Put variable closer to its usages

compiler/fir/raw-fir/raw-fir.common/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt

@@ -547,6 +547,7 @@ abstract class BaseFirBuilder<T>(val baseSession: FirSession, val context: Conte
                 resultInitializer
             )
 
+            fun appendAssignment() {
                 val assignment = unwrappedReceiver.generateAssignment(
                     desugaredSource,
                     null,
@@ -560,7 +561,6 @@ abstract class BaseFirBuilder<T>(val baseSession: FirSession, val context: Conte
                     convert
                 )
 
-            fun appendAssignment() {
                 if (assignment is FirBlock) {
                     statements += assignment.statements
                 } else {