fix a braino in ia64 uaccess csum changes

Fixes: cc03f19c (ia64: csum_partial_copy_nocheck(): don't abuse csum_partial_copy_from_user())
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>