KVM: x86: Fix ERAPS RAP clear on INVPCID single-context invalidation

KVM: x86: Fix ERAPS RAP clear on INVPCID single-context invalidation

Use kvm_register_mark_dirty() instead of kvm_register_is_dirty() to
actually mark VCPU_EXREG_ERAPS as dirty when emulating
INVPCID_TYPE_SINGLE_CTXT.  kvm_register_is_dirty() is a read-only
predicate whose return value is discarded, making the call a no-op.
Without this fix, a single-context INVPCID will not trigger a RAP clear
on the next VMRUN, breaking the ERAPS security guarantee.

Fixes: db5e82496492 ("KVM: SVM: Virtualize and advertise support for ERAPS")
Signed-off-by: Emily Ehlert <ehemily@amazon.de>
Link: https://patch.msgid.link/20260518135956.82569-1-ehemily@amazon.de
Signed-off-by: Sean Christopherson <seanjc@google.com>