vala: Fix return-type of BasicBlock.get_successors()
vala: Fix return-type of BasicBlock.get_successors()

https://bugzilla.gnome.org/show_bug.cgi?id=794979

frida/vala,frida/vala,GNOME/vala,frida/vala,frida/vala,frida/vala,GNOME/vala,GNOME/vala,GNOME/vala