Use default strides in allocated buffer in h264 encoder wrapper

The explicit values were incorrect: u/v strides were half-width rounded
down, but it has to be rounded up: for odd resolutions there are supposed to be extra u/v samples for last odd pixels.

Bug: chromium:542449805
Change-Id: I06f85d4cba737f69699f056057ebf039094bbffe
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/493940
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Auto-Submit: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48298}