ada: Fix bogus error on allocator in instantiation with private derived types

ada: Fix bogus error on allocator in instantiation with private derived types

The problem is that the call to Convert_View made from Make_Init_Call does
nothing because the Etype is not set on the second argument.

gcc/ada/

	* exp_ch7.adb (Convert_View): Add third parameter Typ and use it if
	the second parameter does not have an Etype.
	(Make_Adjust_Call): Remove obsolete setting of Etype and pass Typ in
	call to Convert_View.
	(Make_Final_Call): Likewise.
	(Make_Init_Call): Pass Typ in call to Convert_View.