KVM: Fix VM exit code for full dirty ring in API documentation

KVM: Fix VM exit code for full dirty ring in API documentation

While reading the documentation, I saw a exit code I could not grep for, to
figure out it has a slightly different name.

Fix that name in documentation so it points to the right exit code.

Signed-off-by: Leonardo Bras <leo.bras@arm.com>
Link: https://lore.kernel.org/r/20251014152802.13563-1-leo.bras@arm.com
Signed-off-by: Sean Christopherson <seanjc@google.com>