Fix compile error when LOG_NDEBUG enabled

Bug: 16977404
Change-Id: Ia7d6ea00d7b89ba10ff70f542b5f4c7ed2c2147e
diff --git a/media/libnbaio/MonoPipeReader.cpp b/media/libnbaio/MonoPipeReader.cpp
index de82229..e4d3ed8 100644
--- a/media/libnbaio/MonoPipeReader.cpp
+++ b/media/libnbaio/MonoPipeReader.cpp
@@ -39,7 +39,7 @@
         return NEGOTIATE;
     }
     ssize_t ret = android_atomic_acquire_load(&mPipe->mRear) - mPipe->mFront;
-    ALOG_ASSERT((0 <= ret) && (ret <= mMaxFrames));
+    ALOG_ASSERT((0 <= ret) && ((size_t) ret <= mPipe->mMaxFrames));
     return ret;
 }