ace_of_penguins: add dependency on host-libpng

libpng is needed on the host to build the make-imglib utility, built
during the compilation of ace_of_penguins for the target.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/games/ace_of_penguins/ace_of_penguins.mk

@@ -10,6 +10,6 @@ ACE_OF_PENGUINS_AUTORECONF = YES
 ACE_OF_PENGUINS_STAGING = NO
 ACE_OF_PENGUINS_TARGET = YES
 
-ACE_OF_PENGUINS_DEPENDENCIES = libpng xserver_xorg-server xlib_libXpm
+ACE_OF_PENGUINS_DEPENDENCIES = libpng host-libpng xserver_xorg-server xlib_libXpm
 
 $(eval $(call AUTOTARGETS,package/games,ace_of_penguins))