Psi2ir: fix function type check for fun interface conversion

Parameter of a synthetic SAM adapter always has a function type (not a
subtype). Checking for the subtypes broke the case from KT-46908, where
fun interface is itself a subtype of a function type.

 #KT-46908 Fixed

compiler/testData/codegen/box/funInterface/kt46908_functionSupertype.kt

@@ -0,0 +1,18 @@
+// IGNORE_BACKEND: JS, JS_IR, WASM
+
+fun interface Foo : () -> Int
+
+fun id(foo: Foo): Any = foo
+
+fun box(): String {
+    val p1 = object : Foo {
+        override fun invoke(): Int = 42
+        override fun toString(): String = "OK"
+    }
+    val p2 = id(p1)
+
+    if (p1 !== p2) return "Fail identity equals"
+    if (p1.toString() != p2.toString()) return "Fail toString"
+
+    return p2.toString()
+}