media/gpu/V4L2SVD: Set initial value of arguments at header file.

This CL set the initial value of some arguments at header file, to
prevent use-before-initialization error.

BUG=none
TEST=./video_decode_acclerator_tests

Change-Id: I695be14c2bea09c53c966d35034827748c426ae6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1716446
Commit-Queue: Chih-Yu Huang <akahuang@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680717}
2 files changed