linker_config_src in filesystem may read filegroup

Add "path" annotation to the linker_config_src property in filesystem
module to read a filegroup as a source.

Bug: 365670526
Test: lunch aosp_cf_x86_64_phone_soong_system-trunk_staging-userdebug
      && m
Change-Id: I96abb376640eea009f03841866b8c7b5d95917fa
diff --git a/filesystem/system_image.go b/filesystem/system_image.go
index a8fd368..805249e 100644
--- a/filesystem/system_image.go
+++ b/filesystem/system_image.go
@@ -27,7 +27,7 @@
 
 type systemImageProperties struct {
 	// Path to the input linker config json file.
-	Linker_config_src *string
+	Linker_config_src *string `android:"path"`
 }
 
 // android_system_image is a specialization of android_filesystem for the 'system' partition.