Fix broken CleanSpec.mk in libs/gui

The CleanSpec is missing parens, which causes $P to be interpreted as a
single variable, and the following printed to the log:

Clean step: rm -rf RODUCT_OUT/obj/SHARED_LIBRARIES/libgui_intermediates

This patch adds parens as needed.

Change-Id: I587998fa67a4884418c286360a577cdbb6ea9a21
diff --git a/libs/gui/CleanSpec.mk b/libs/gui/CleanSpec.mk
index 0d08291..c062229 100644
--- a/libs/gui/CleanSpec.mk
+++ b/libs/gui/CleanSpec.mk
@@ -48,4 +48,4 @@
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************
 $(call add-clean-step, find $(PRODUCT_OUT) -type f -name "libgui*" -print0 | xargs -0 rm -f)
-$(call add-clean-step, rm -rf $PRODUCT_OUT/obj/SHARED_LIBRARIES/libgui_intermediates)
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/obj/SHARED_LIBRARIES/libgui_intermediates)