KVM: x86/mmu: Drop ignored return value from kvm_tdp_mmu_clear_dirty_slot()

Drop the return value from kvm_tdp_mmu_clear_dirty_slot() as its sole
caller ignores the result (KVM flushes after clearing dirty logs based on
the logs themselves, not based on SPTEs).

Cc: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20241011021051.1557902-7-seanjc@google.com


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