Revert "KVM: Eliminate extra function calls in kvm_get_dirty_log_protect()"

The value of "dirty_bitmap[i]" is already check before setting its value
to mask. The following check of "mask" is redundant. The check of "mask" was
introduced by commit 58d2930f ("KVM: Eliminate extra function calls in
kvm_get_dirty_log_protect()"), revert it.
Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -1205,11 +1205,9 @@ int kvm_get_dirty_log_protect(struct kvm *kvm,
 			mask = xchg(&dirty_bitmap[i], 0);
 			dirty_bitmap_buffer[i] = mask;
 
-			if (mask) {
-				offset = i * BITS_PER_LONG;
-				kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
-									offset, mask);
-			}
+			offset = i * BITS_PER_LONG;
+			kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
+								offset, mask);
 		}
 		spin_unlock(&kvm->mmu_lock);
 	}