Change main code image filename in CC3200 bundles

/sys/mcuimg.bin is just another file on SLFS, no reason to give it
special treatment. Preserve backward compatibility with old bundles:
translate sys_mcuimg.bin -> /sys/mcuimg.bin

PUBLISHED_FROM=be89a3d9785046f09279fef9e2bb6604eeaa576e

examples/CC3200/Makefile.build

@@ -66,7 +66,7 @@ $(FW_ZIP): $(FW_ELF) $(FW_BIN) $(SLFS_FILES)
 	  --build_info=$(BUILD_INFO_JSON) \
 	  --output=$(FW_MANIFEST) \
 	  --src_dir=$(FW_DIR) \
-	  sys_mcuimg.bin:src=$(notdir $(FW_BIN)) \
+	  /sys/mcuimg.bin:src=$(notdir $(FW_BIN)) \
 		$(foreach f,$(SLFS_FILES), $(notdir $(f)):src=$(notdir $(f)))
 	@echo "  ZIP   $@"
 	@fw_meta create_fw \