media: ipu3-cio2: Simplify cleanup code

The code looks more nicer if we use:
	while (i--)
instead:
	for (i = i - 1; i >= 0; i--)

This would also allow making 'i' unsigned again.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>