media/gpu/vaapi: Fix compile error due to VA_FOURCC_NV12 type

crrev.com/c/2041382 can cause a type difference error on some
build environment. This fixes the compile error.

Bug: 1057857, 1050377
Test: Compile chrome
Change-Id: Ia4e20a3f19599f0b849d591ac07d043ce16ef84d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2082429
Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/branch-heads/4044@{#619}
Cr-Branched-From: a6d9daf149a473ceea37f629c41d4527bf2055bd-refs/heads/master@{#737173}
1 file changed