Caught with clang -Wextra.

Bug: b/150155499
Change-Id: I80bdcaeb7f11954e57fd6e27d8747625eba66694
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/43990
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Presubmit-Ready: Ben Clayton <bclayton@google.com>