No behavior is modified in this cl. log2() was calling logarithm2()
with the wrong options, but logarithm2() currently ignores all
options, so this had no consequence. Fixing to prevent future errors.

Change-Id: I6518d9d90fc1f34cadab2de12657064b2510b463
Reviewed-on: https://swiftshader-review.googlesource.com/10429Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>