staging: comedi: comedi_fops.c: added casts to get rid of sparse warnings

fixed sparse warnings by adding a cast in assignment from
void [noderef] __user * to unsigned int __force *
and a reverse cast in argument from
unsigned int * to  unsigned int __user * .

Signed-off-by: B K Karthik <karthik.bk2000@live.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20200717103031.3mfnlvqo3waolsee@pesu-pes-edu


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>