C2AllocatorGralloc: Convert C2Rect to Rect correctly

The field of C2Rect is (left, top, width, height), and the field of
Rect is (left, top, right, bottom). This CL fixes the conversion from
C2Rect to Rect.

Bug: 170697563
Test: android.media.cts.MediaCodecBlockModelTest#testDecodeShortAudio

Change-Id: I74c7197587fbdaa0916046d1a9fad24d00e4f7a3
(cherry picked from commit 3d0e82ce1b1d1c594fee6796f49509bef5be9ca2)