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.com


Signed-off-by: Sean Christopherson <seanjc@google.com>