random: wire up fops->splice_{read,write}_iter()

stable inclusion
from stable-v5.10.119
commit 18c261e9485a238129b857a8e53d3e2da8ca8246
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18c261e9485a238129b857a8e53d3e2da8ca8246



--------------------------------

commit 79025e72 upstream.

Now that random/urandom is using {read,write}_iter, we can wire it up to
using the generic splice handlers.

Fixes: 36e2c742 ("fs: don't allow splice read/write without explicit ops")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[Jason: added the splice_write path. Note that sendfile() and such still
 does not work for read, though it does for write, because of a file
 type restriction in splice_direct_to_actor(), which I'll address
 separately.]
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>