TARGET_FS_CONFIG_GEN is a list, not a single path

Bug: 130787336
Test: m oemaids_header_gen oemaids_headers passwd group
Test: Set TARGET_FS_CONFIG_GEN to a list of paths
Change-Id: Ic1f7d38239f3f805ca0723c24005d3e18a811870
diff --git a/android/variable.go b/android/variable.go
index 666f29f..f3da66d 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -288,7 +288,7 @@
 	ProductHiddenAPIStubsSystem []string `json:",omitempty"`
 	ProductHiddenAPIStubsTest   []string `json:",omitempty"`
 
-	TargetFSConfigGen *string `json:",omitempty"`
+	TargetFSConfigGen []string `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {