random: re-add removed comment about get_random_{u32,u64} reseeding

stable inclusion
from stable-v5.10.119
commit bb563d06c5bc3d08bd5c8665d6b1da6865114cfd
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=bb563d06c5bc3d08bd5c8665d6b1da6865114cfd



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

commit dd7aa36e upstream.

The comment about get_random_{u32,u64}() not invoking reseeding got
added in an unrelated commit, that then was recently reverted by
0313bc27 ("Revert "random: block in /dev/urandom""). So this adds
that little comment snippet back, and improves the wording a bit too.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
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>