V4L2EncodeComponent: Better error handling when syncing buffer

Thanks Yiwei pointed out the buggy code which doesn't do error handling
and also we should only sync CPU writable buffer.

Bug: 268317650
Test: atest com.google.android.media.gts.RtcVideoCodecTest#testDynamicBitrateChangeVp8
Change-Id: I3c1019fb0d56180ef8460625843cf8e98301ddce