[Ada] Crash on subtype of fixed-point type

[Ada] Crash on subtype of fixed-point type

gcc/ada/

	* freeze.adb (Freeze_Fixed_Point_Type): Do not scale the bounds
	of a declared subtype using the 'Small of the type;  this is
	done during resolution of the bound itself, unlike what is done
	for the bounds of the base type, which are used to determine its
	required size. Previous code performed this scaling twice,
	leading to meaningless values for such a subtype.