Documentation: KVM: make corrections to halt-polling.rst

Documentation: KVM: make corrections to halt-polling.rst

Module parameters are in sysfs, not debugfs, so change that.

Remove superfluous "that" following "Note:".
Hyphenate "system-wide" values.
Hyphenate "trade-off".

Don't treat "denial of service" as a verb.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230612030810.23376-2-rdunlap@infradead.org