In 821601ea (Make VNC support optional)
cocoa.o was moved from ui-obj-$(CONFIG_COCOA) to vnc-obj-$(CONFIG_COCOA),
adding a dependency on $(CONFIG_VNC). That must've been unintentional.

Cc: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>