[media] v4l2-ioctl.c: fix sparse __user-related warnings

[media] v4l2-ioctl.c: fix sparse __user-related warnings

Fix the use of __user in the check_array_args() prototype: instead of
using 'void * __user *' you should use 'void __user **' for sparse to
understand this correctly.

This also required the use of __force in the '*kernel_ptr = user_ptr'
assignment.

Also replace a wrong cast (void *) with the correct one (void **)
in check_array_args().

This fixes these sparse warnings:

drivers/media/v4l2-core/v4l2-ioctl.c:2284:35: warning: incorrect type in assignment (different address spaces)
drivers/media/v4l2-core/v4l2-ioctl.c:2301:35: warning: incorrect type in assignment (different address spaces)
drivers/media/v4l2-core/v4l2-ioctl.c:2319:35: warning: incorrect type in assignment (different address spaces)
drivers/media/v4l2-core/v4l2-ioctl.c:2386:57: warning: incorrect type in argument 4 (different address spaces)
drivers/media/v4l2-core/v4l2-ioctl.c:2420:29: warning: incorrect type in assignment (different address spaces)

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>