KVM: x86: Replace BUG_ON() with WARN_ON_ONCE() on "bad" nested GPA translation

KVM: x86: Replace BUG_ON() with WARN_ON_ONCE() on "bad" nested GPA translation

If KVM attempts to translate what it thinks is an L2 GPA with a non-nested
MMU, simply WARN and return the GPA, i.e. trust the MMU more than the
caller, as there is zero reason to potentially panic the host kernel just
because KVM misused an API.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260618185746.2023283-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>