Super accessor from within an inner class failing from TASTY

[nicolasstucki]

package a {
  class PolyA {
    protected def m(): Unit = ()
  }
}

class X extends a.PolyA {
  trait Inner {
    m()
  }
}

which can be reproduced with

dotc -d out <sourceAbove>
dotc -from-tasty -Ycheck:elimJavaPackages,refchecks,splitter,arrayConstructors,erasure,capturedVars,getClass,elimStaticThis,labelDef -classpath out X a.PolyA 

and fails with

checking out2/a/PolyA.class after phase MegaPhase{checkStatic, elimRepeated, normalizeFlags, extmethods, expandSAMs, tailrec, byNameClosures, liftTry, hoistSuperArgs, classOf, refchecks}
Exception in thread "main" java.lang.AssertionError: assertion failed: method super$m is both Deferred and Private
	at scala.Predef$.assert(Predef.scala:219)
	at dotty.tools.dotc.transform.TreeChecker.transformSym(TreeChecker.scala:95)
	at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform(DenotTransformers.scala:68)
	at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform$(DenotTransformers.scala:67)
	at dotty.tools.dotc.transform.TreeChecker.transform(TreeChecker.scala:48)
	at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:872)
	at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:432)
	at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:427)
	at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:421)
	at dotty.tools.dotc.core.Symbols$.toDenot(Symbols.scala:684)
	at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1(SymDenotations.scala:1765)
	at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1$adapted(SymDenotations.scala:1765)
	at dotty.tools.dotc.core.Scopes$Scope.filter(Scopes.scala:104)
	at dotty.tools.dotc.core.SymDenotations$ClassDenotation.paramAccessors(SymDenotations.scala:1765)
	at dotty.tools.dotc.core.Contexts$Context.superCallContext(Contexts.scala:328)
...

[nicolasstucki]

Test file tests/run/protectedacc.scala from #3715 contains this code.

[odersky]

Fixed by #3715