There was an ambiguous type warning between Float4 and RValue<Float4>.

Change-Id: I526fc2430a66b8545e81fe5ae97fb423e7f01aec
Reviewed-on: https://swiftshader-review.googlesource.com/7356Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>