random: fix soft lockup when trying to read from an uninitialized blocking pool

mainline inclusion
from mainline-v5.2-rc2
commit 58be0106
category: bugfix
bugzilla: NA
CVE: NA

https://gitee.com/openeuler/kernel/issues/I1CVQ4?from=project-issue


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Fixes: eb9d1bf0: "random: only read from /dev/random after its pool has received 128 bits"
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>