zlib: install using cp instead of install for zlib libraries

This patch will install zlib keeping the symlinks. The usage of
$(INSTALL) here did not take into account symbolic links.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

package/zlib/zlib.mk

@@ -53,7 +53,7 @@ $(STAGING_DIR)/usr/lib/libz.a: $(ZLIB_DIR)/libz.a
 	touch -c $@
 
 $(STAGING_DIR)/usr/lib/libz.so: $(STAGING_DIR)/usr/lib/libz.a
-	$(INSTALL) $(ZLIB_DIR)/libz.so* $(STAGING_DIR)/usr/lib/
+	cp -dpf $(ZLIB_DIR)/libz.so* $(STAGING_DIR)/usr/lib/
 	touch -c $@
 
 $(TARGET_DIR)/usr/lib/libz.so: $(STAGING_DIR)/usr/lib/libz.so