Documentation/hw-vuln: Fix rST warning

mainline inclusion
from mainline-v6.2
commit 971cecb9
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6FB6C
CVE: CVE-2022-27672

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=971cecb9591a7b8ceae658252bf15240d7078a45



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

The following warning:

   Documentation/admin-guide/hw-vuln/cross-thread-rsb.rst:92: ERROR: Unexpected indentation.

was introduced by commit 493a2c2d.  Fix it by placing everything in
the same paragraph and also use a monospace font.

Fixes: 493a2c2d ("Documentation/hw-vuln: Add documentation for Cross-Thread Return Predictions")
Reported-by: Stephen Rothwell <sfr@canb@auug.org.au>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Guo Mengqi <guomengqi3@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>