extract_utils: fix empty shared_libs for libraries without any

A case where this happens is with NXP firmware installed under
/vendor/lib[64].

Change-Id: Ie31d6e12d1ec5a7e7148fd2c883f3a389d9368b9

Author: AKoskovich

extract_utils/bp_builder.py

@@ -223,7 +223,7 @@ def target(
         arch = MACHINE_TARGET_MAP[machine]
         target[arch] = {'srcs': [rel_path]}
 
-        if deps is not None:
+        if deps:
             target[arch]['shared_libs'] = deps
 
         return self