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
diff --git a/media/codec2/sfplugin/CCodecConfig.cpp b/media/codec2/sfplugin/CCodecConfig.cpp
index a943626..897a696 100644
--- a/media/codec2/sfplugin/CCodecConfig.cpp
+++ b/media/codec2/sfplugin/CCodecConfig.cpp
@@ -1907,7 +1907,7 @@
                         bottom = c2_min(bottom, height);
                         if (right > left && bottom > top) {
                             C2Rect rect(right - left, bottom - top);
-                            rect.at(left, top);
+                            rect = rect.at(left, top);
                             c2QpOffsetRects.push_back(C2QpOffsetRectStruct(rect, offset));
                         } else {
                             ALOGE("Rects configuration %s is not valid.", box);