Documentation/hw-vuln: Fix rST warning

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: NPaolo Bonzini <pbonzini@redhat.com>

Documentation/admin-guide/hw-vuln/cross-thread-rsb.rst

@@ -88,5 +88,4 @@ capability to override those interceptions, but since this is not common, the
 mitigation that covers this path is not enabled by default.
 
 The mitigation for the KVM_CAP_X86_DISABLE_EXITS capability can be turned on
-using the boolean module parameter mitigate_smt_rsb, e.g.:
-        kvm.mitigate_smt_rsb=1
+using the boolean module parameter mitigate_smt_rsb, e.g. ``kvm.mitigate_smt_rsb=1``.