s390/uaccess: normalize order of parameters of indirect uaccess function calls

For some unknown reason the indirect uaccess functions on s390 implement a
different parameter order than what is usual.

e.g.:

unsigned long copy_to_user(void *to, const void *from, unsigned long n);
vs.
size_t (*copy_to_user)(size_t n, void __user * to, const void *from);

Let's get rid of this confusing parameter reordering.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>