codec2: Fix VideoEncoderRoiTest cts failure

Corrected the assignment of rect to ensure proper region of interest
configuration, preventing invalid rects and fixing the test failure.

Test:run cts --abi arm64-v8a -m CtsVideoCodecTestCases -t android.videocodec.ctsVideoEncoderRoiTest --log-level-display INFO

Bug: 374920078

Change-Id: Ia0ab535c2671ce0f85688ec028c53dfd5d922cad