Fix sdk aidl include for droiddoc

Prior to this change droidstubs modules that set sdk_version
did not get framework.aidl added to its aidl includes.

Bug: 149138391
Test: patch CL in bug && m system_aidl_test-droidstubs
Change-Id: I92ab344c8a4311e10c1e5c8ebf525fa2dc704075
(cherry picked from commit f278ca60e06da86c67f6a3865c290f8451657ce9)
diff --git a/java/droiddoc.go b/java/droiddoc.go
index 098400b..959f1c7 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -534,6 +534,9 @@
 		ctx.AddMissingDependencies(sdkDep.java9Classpath)
 	} else if sdkDep.useFiles {
 		deps.bootClasspath = append(deps.bootClasspath, sdkDep.jars...)
+		deps.aidlPreprocess = sdkDep.aidl
+	} else {
+		deps.aidlPreprocess = sdkDep.aidl
 	}
 
 	ctx.VisitDirectDeps(func(module android.Module) {