This is a Randomized, Double-Blind, Placebo-Controlled, Parallel-Design, Multiple-Site Clinical Study to Evaluate the Therapeutic Equivalence of Diclofenac Sodium Gel, 1% (Glenmark Pharmaceuticals Ltd) to Voltaren® Gel (Diclofenac Sodium topical gel) 1% (Novartis Consumer Health, Inc) in Patients with Osteoarthritis (OA) of the Knee