ada: Fix bug in overloaded selected_components in aspect_specifications

ada: Fix bug in overloaded selected_components in aspect_specifications

This patch fixes a bug where if a selected_component X.Y appears in an
aspect_specification, and there are two or more overloaded Y's in X,
then it can choose the wrong one, leading to subsequent type errors.
It was always picking the last declaration of Y, and leaving Entity
set to that. We now reset Entity (as for the already-existing code
for N_Identifier just below).

Note that Resolve_Aspect_Expressions is called only for
aspect_specifications, and not even all aspect_specifications,
so the bug didn't occur for other names. For example,
Resolve_Aspect_Expressions is not called for aspect_specifications
in the visible part of a library package if there is no private part.

gcc/ada/

	* sem_ch13.adb (Resolve_Name): This is called only for names in
	aspect_specifications. If the name is an overloaded
	selected_component, reset the Entity. Note that this was already
	done for N_Identifier in the code just below.