A Phase 3, 12-Week, Double-Blind, Randomized, Parallel-Group, Multicenter Study Investigating the Efficacy and Safety of Symbicort pMDI 80/2.25 μg, 2 Actuations Twice Daily, and Symbicort pMDI 80/4.5 μg, 2 Actuations Twice Daily, Compared with Budesonide pMDI 80 μg, 2 Actuations Twice Daily, in Children Ages 6 to \<12 Years with Asthma