Firefighters Saturday knocked down a brush fire near Warner Bros. Studios, which they held to a quarter-acre. The blaze was reported about 9:20 p.m. Saturday at 6700 W. Forest Lawn Drive, between West Olive Avenue and Gate 9 of the studios, and just south of the Los Angeles River, according to the Los Angeles Fire Department’s Jennifer Middleton. It took 42 firefighters less just over 40 minutes to extinguish the fire, she said. No structures we…