Handle MODULE_LICENSE_MPL the same as MODULE_LICENSE_GPL.

Change-Id: Iefc6df3f3401a591f53ec3f22202044c60acf460
diff --git a/core/definitions.mk b/core/definitions.mk
index 2875e28..6db9d8f 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -339,7 +339,7 @@
 
 define find-parent-file
 $(strip \
-  $(eval _fpf := $(wildcard $(strip $(1))/$(strip $(2)))) \
+  $(eval _fpf := $(wildcard $(foreach f, $(2), $(strip $(1))/$(f)))) \
   $(if $(_fpf),$(_fpf), \
        $(if $(filter-out ./ .,$(1)), \
              $(call find-parent-file,$(patsubst %/,%,$(dir $(1))),$(2)) \