Fix minor build error

We should point the build at the one root Rust source file for a
library/module, not all the sources.

This is mostly harmless, except it confuses rust-analyzer, and masks
an error in lib.rs.

Test: Builds
Change-Id: Ief5149e0c56feeb132b3b381bd8c255bb1a3e393
diff --git a/vm_payload/Android.bp b/vm_payload/Android.bp
index 7f2b9df..286612c 100644
--- a/vm_payload/Android.bp
+++ b/vm_payload/Android.bp
@@ -8,7 +8,7 @@
     crate_name: "vm_payload",
     defaults: ["avf_build_flags_rust"],
     visibility: ["//visibility:private"],
-    srcs: ["src/*.rs"],
+    srcs: ["src/lib.rs"],
     include_dirs: ["include"],
     prefer_rlib: true,
     rustlibs: [