rust: Fix indentation, convert to TABs

The two “rust_ffi_host” modules looked different in my editor because
one was indented with TABs and the other with spaces. They now
consistently use spaces (like the other examples in this file).

Test: atest
Change-Id: I7d0cdba5978da92a1a299bb290472403d4f13462

rust/library_test.go

@@ -30,11 +30,11 @@ func TestLibraryVariants(t *testing.T) {
 			srcs: ["foo.rs"],
 			crate_name: "foo",
 		}
-                rust_ffi_host {
-                        name: "libfoo.ffi",
-                        srcs: ["foo.rs"],
-                        crate_name: "foo"
-                }`)
+		rust_ffi_host {
+			name: "libfoo.ffi",
+			srcs: ["foo.rs"],
+			crate_name: "foo"
+		}`)
 
 	// Test all variants are being built.
 	libfooRlib := ctx.ModuleForTests("libfoo", "linux_glibc_x86_64_rlib_rlib-std").Rule("rustc")