sparc: switch to providing csum_and_copy_from_user()

sparc64 already is equivalent to that (trivial access_ok());
add it into sparc32 csum_partial_copy_from_user() and we can
rename both to csum_and_copy_fromUser() and be done with that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>