V4L2DecodeInterface: use correct picture size to calculate size of input buffers

This CL removes unused variables at V4L2DecodeInterface, and uses the
correct picture size to calculate the size of input buffers.

Bug: 175270843
Test: com.google.android.media.gts.WidevineH264PlaybackTests#testCbcsL1WithUHD30
Change-Id: Ieaf4ee4355d462f9f70f890ef8dd2e140ac33771
diff --git a/components/V4L2DecodeInterface.cpp b/components/V4L2DecodeInterface.cpp
index dc466d5..b0f677b 100644
--- a/components/V4L2DecodeInterface.cpp
+++ b/components/V4L2DecodeInterface.cpp
@@ -318,7 +318,7 @@
 }
 
 size_t V4L2DecodeInterface::getInputBufferSize() const {
-    return calculateInputBufferSize(getMaxSize().GetArea());
+    return calculateInputBufferSize(mSize->width * mSize->height);
 }
 
 c2_status_t V4L2DecodeInterface::queryColorAspects(