Add a missing reader barrier in entrypoint stub

Also refactored some comments.

Change-Id: I5c50f487bf9d71f1be5f6c8814bf039993fc1267
diff --git a/runtime/arch/mips/quick_entrypoints_mips.S b/runtime/arch/mips/quick_entrypoints_mips.S
index 4d5004f..88182dd 100644
--- a/runtime/arch/mips/quick_entrypoints_mips.S
+++ b/runtime/arch/mips/quick_entrypoints_mips.S
@@ -659,7 +659,7 @@
     sw     $a0, 0($sp)
     .cfi_rel_offset 4, 0
 
-    # move $a0, $a0                 # pass ref in a0 (no-op for now since parameter ref is unused)
+    # move $a0, \rRef               # pass ref in a0 (no-op for now since parameter ref is unused)
     .ifnc \rObj, $a1
         move $a1, \rObj             # pass rObj
     .endif