fixing slight perf drop issue due to blanket barrier statement
fixing slight perf drop issue due to blanket barrier statement

kknox/clFFT,liebharc/clFFT,kknox/clFFT,liebharc/clFFT,ghisvail/clFFT,kknox/clFFT,9prady9/clFFT,liebharc/clFFT,arrayfire/clFFT,ghisvail/clFFT,arrayfire/clFFT,liebharc/clFFT,9prady9/clFFT,9prady9/clFFT,arrayfire/clFFT,clMathLibraries/clFFT,clMathLibraries/clFFT,ghisvail/clFFT,clMathLibraries/clFFT