staging: xillybus: Use devm_kcalloc() for arrays

Replace devm_kzalloc where it applies.

Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>