KVM: Add the missed title format

The 7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 now is not a title, make it
as a title to keep the format consistent.
Signed-off-by: Shaoqin Huang <shahuang@redhat.com>
Fixes: 106ee47d ("docs: kvm: Convert api.txt to ReST format")
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20230220034910.11024-1-shahuang@redhat.comSigned-off-by: Sean Christopherson <seanjc@google.com>

Documentation/virt/kvm/api.rst

@@ -7267,6 +7267,7 @@ and injected exceptions.
        will clear DR6.RTM.
 
 7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
+--------------------------------------
 
 :Architectures: x86, arm64, mips
 :Parameters: args[0] whether feature should be enabled or not