OCL: fixed some ocl tests from imgproc (test_loop_times = 30)

fixed tests for:
* Filter2D
* MatchTemplate
* CalcBackProject

test_modules=imgproc
build_examples=OFF
check_regression=OCL*Filter2D*:OCL*MatchTemplate*:OCL*CalcBackProject*
test_filter=OCL*Filter2D*:OCL*MatchTemplate*:OCL*CalcBackProject*