T-API: eliminated restriction delta == 0 from cv::sepFilter2D

test_modules=imgproc
test_filter=*OCL*Sobel*:*OCL*Scharr*:*OCL*Canny*:*OCL*GaussianBlur*:*OCL*SepFilter2D*:*OCL*Corner*
build_examples=OFF
check_regression=OCL*Sobel:OCL*Scharr:OCL*Canny:OCL*GaussianBlur:OCL*SepFilter2D:OCL*Corner*