Limit find-copy-subdir-files to just files

This is used to add entries to PRODUCT_COPY_FILES -- those should always
be files, not directories or anything else special.

Bug: 30482029
Change-Id: I2691ae81c344c22e518c6b10cd485c73d654a03b
diff --git a/core/product_config.mk b/core/product_config.mk
index 0d4ced3..6438d51 100644
--- a/core/product_config.mk
+++ b/core/product_config.mk
@@ -74,7 +74,7 @@
 ###########################################################
 
 define find-copy-subdir-files
-$(shell find $(2) -name "$(1)" | $(SED_EXTENDED) "s:($(2)/?(.*)):\\1\\:$(3)/\\2:" | sed "s://:/:g")
+$(sort $(shell find $(2) -name "$(1)" -type f | $(SED_EXTENDED) "s:($(2)/?(.*)):\\1\\:$(3)/\\2:" | sed "s://:/:g"))
 endef
 
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