Fix incorrect output in Python tutorial, lesson 5

[qqaatw]

This is column-major so y should vary faster than x.

The equivalent c++ code:

Halide/tutorial/lesson_05_scheduling_1.cpp

Lines 97 to 101 in a6f5ca4

	for (int x = 0; x < 4; x++) {
	for (int y = 0; y < 4; y++) {
	printf("Evaluating at x = %d, y = %d: %d\n", x, y, x + y);
	}
	}

[abadams]

Nice catch, thanks