Add missing comma, introduced in 9c14bda0

Bug: none
Change-Id: Iffbe771b6c6af408c2c809e9beef694543554aa4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48748Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>