[NET]: SPARC checksum annotations and cleanups.

* sanitize prototypes, annotate
* kill bogus access_ok() in csum_partial_copy_from_user (the only caller checks)
* kill useless shift

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>