Fix: "sp_uuid_list.txt" dependency list

This change makes the target creating the "sp_uuid_list.txt" file
depend on "shared_directory" to ensure the directory actually exists
before usage.

Change-Id: I08cc61963715b4bab0dbaf102117c00e8cefc048
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
diff --git a/fvp_ffa.mk b/fvp_ffa.mk
index a800dbd..43e3986 100644
--- a/fvp_ffa.mk
+++ b/fvp_ffa.mk
@@ -255,7 +255,7 @@
 
 ffa-sp-all-clean: sp_uuid_list_clean
 
-$(SHARED_DIR)/sp_uuid_list.txt: ffa-sp-all
+$(SHARED_DIR)/sp_uuid_list.txt: ffa-sp-all | shared_directory
 	find $(TS_INSTALL_PREFIX)/$(SP_DEPLOYMENT_TYPE)/bin -name "[0-9a-f-]*.$(SP_FILE_EXTENSION)" -type f | \
 		sed -n "s@.*/\(.*\).$(SP_FILE_EXTENSION)@\1@gp" | tr '\n' ',' | \
 		head -c -1 > $(SHARED_DIR)/sp_uuid_list.txt