Avoid incorrect member reference warning

Change-Id: I6f1b271c3a7b805dd4e539d0d44e2cbc626ef1f7

docs/source/nnls_solving.rst

diff --git a/docs/source/nnls_solving.rst b/docs/source/nnls_solving.rst
index bc0e16a..236af8e 100644
--- a/docs/source/nnls_solving.rst
+++ b/docs/source/nnls_solving.rst
@@ -909,8 +909,8 @@
 iterations are enough, depending upon the conditioning of your
 problem.
 
-If :member:`Solver::Options::max_num_refinement_iterations = 0`, then
-the Gauss-Newton step is computed in single precision.
+If :member:`Solver::Options::max_num_refinement_iterations` is 0, then the
+Gauss-Newton step is computed in single precision.
 
 .. _section-preconditioner: