OCL: [Brute_Force_Match]Remove unnecesary operations and calculations in loop body.

In my atom paltfrom, it show some gains in 
OCL_BruteForceMatcherFixture_Match*
OCL_BruteForceMatcherFixture_RadiusMatch*
OCL_BruteForceMatcherFixture_KnnMatch*

Please help review. Thanks.

check_regression=*OCL*Brute*
test_modules=features2d