bp2build: genrule converter only supports "genrule".

This excludes the bp2build mutator from running for cc_genrule or
java_genrule, which may require alternative implementations.

Test: bp2build; bazel build //bionic/...
Change-Id: Ie14dd6dfa5e806fd6ac6e8f9989356f3880c79bf
diff --git a/genrule/genrule.go b/genrule/genrule.go
index fc6a44f..b43f28e 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -824,6 +824,11 @@
 		return
 	}
 
+	if ctx.ModuleType() != "genrule" {
+		// Not a regular genrule. Could be a cc_genrule or java_genrule.
+		return
+	}
+
 	// Bazel only has the "tools" attribute.
 	tools := android.BazelLabelForModuleDeps(ctx, m.properties.Tools)
 	tool_files := android.BazelLabelForModuleSrc(ctx, m.properties.Tool_files)