Made this change in code review without proper testing.
The "level" being set here was the input argument, rather than the data
member.

Bug: b/145685985
Change-Id: I8641701cc0600837f4dc612d29ffaa4cd63390b1
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39269
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>