Fix the issue of NV12 input with wrong format VPX_IMG_FMT_I420

C2SoftVpxEnc uses NV12 input data but format is specified as I420,
which causes the recorded video messy.

The fix is using mConversionBuffer as input, whose format is I420.

Bug: 139906732
Test:
Change-Id: Ib94dd217a82b2bac57056cfc3af5344da78b47d7
diff --git a/media/codec2/components/vpx/C2SoftVpxEnc.cpp b/media/codec2/components/vpx/C2SoftVpxEnc.cpp
index 6dab70b..ebc7a8f 100644
--- a/media/codec2/components/vpx/C2SoftVpxEnc.cpp
+++ b/media/codec2/components/vpx/C2SoftVpxEnc.cpp
@@ -514,7 +514,7 @@
                         return;
                     }
                     vpx_img_wrap(&raw_frame, VPX_IMG_FMT_I420, stride, vstride,
-                                 mStrideAlign, (uint8_t*)rView->data()[0]);
+                                 mStrideAlign, mConversionBuffer.data());
                     vpx_img_set_rect(&raw_frame, 0, 0, width, height);
                 } else {
                     ALOGE("Conversion buffer is too small: %u x %u for %zu",