drm/i915/selftests: fix subtraction overflow bug

On some machines hole_end can be small enough to cause subtraction
overflow. On the other side (addr + 2 * min_alignment) can overflow
in case of mock tests. This patch should handle both cases.

Fixes: e1c5f75 ("drm/i915: Avoid overflow in computing pot_hole loop termination")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3674
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220624113528.2159210-1-andrzej.hajda@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
(cherry picked from commit ab3edc6)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Author: ahajda

drivers/gpu/drm/i915/selftests/i915_gem_gtt.c

@@ -742,7 +742,7 @@ static int pot_hole(struct i915_address_space *vm,
 		u64 addr;
 
 		for (addr = round_up(hole_start + min_alignment, step) - min_alignment;
-		     addr <= round_down(hole_end - (2 * min_alignment), step) - min_alignment;
+		     hole_end > addr && hole_end - addr >= 2 * min_alignment;
 		     addr += step) {
 			err = i915_vma_pin(vma, 0, 0, addr | flags);
 			if (err) {