Build 64-bit drmserver on 64-bit-only

Bug: 158659480
Change-Id: I56cd6df1889e8d479d3f05a3848070e93cff3745
diff --git a/drm/drmserver/Android.bp b/drm/drmserver/Android.bp
index c25a0a1..a9be047 100644
--- a/drm/drmserver/Android.bp
+++ b/drm/drmserver/Android.bp
@@ -40,7 +40,7 @@
         "-Werror",
     ],
 
-    compile_multilib: "32",
+    compile_multilib: "prefer32",
 
     init_rc: ["drmserver.rc"],
 }