OCL: fixed dft calls for matchTemplate

**WIP**
Used R2C dft instead of R2R, because ocl_mulSpectrums works only with 2 channels.

Performance report:
http://ocl.itseez.com/intel/export/perf/pr/3084/report/

check_regression=OCL*MatchTemplate*
test_filter=OCL*MatchTemplate*
test_modules=imgproc
build_examples=OFF