nanohub: expand scanned directory subtree

this takes care of cases when multiple variant configs
are kept in the same place

Bug: 30924350
Change-Id: I3a753aadebef14d507b9273786545d2a1a453f09
Signed-off-by: Alexey Polyudov <apolyudov@google.com>
diff --git a/firmware/app/app.mk b/firmware/app/app.mk
index 349f60c..f2cd9db 100644
--- a/firmware/app/app.mk
+++ b/firmware/app/app.mk
@@ -46,7 +46,7 @@
 # - explicitly provided in VARIANT_CONFIG_PATH (path, where <variant>_conf.mk is located)
 #
 ifeq ($(VARIANT_CONFIG_PATH),)
-  variant_conf := $(wildcard $(TOP_ABSPATH)/vendor/*/$(VARIANT)/nanohub/$(VARIANT)_conf.mk)
+  variant_conf := $(wildcard $(TOP_ABSPATH)/vendor/*/*/nanohub/$(VARIANT)_conf.mk)
   ifeq ($(words $(variant_conf)),1)
     VARIANT_CONFIG_PATH := $(patsubst $(TOP_ABSPATH)/%/$(VARIANT)_conf.mk,%,$(variant_conf))
   else