KVM: x86: remove check on nr_mmu_pages in kvm_arch_commit_memory_region()

* nr_mmu_pages would be non-zero only if kvm->arch.n_requested_mmu_pages is
non-zero.

* nr_mmu_pages is always non-zero, since kvm_mmu_calculate_mmu_pages()
never return zero.

Based on these two reasons, we can merge the two *if* clause and use the
return value from kvm_mmu_calculate_mmu_pages() directly. This simplify
the code and also eliminate the possibility for reader to believe
nr_mmu_pages would be zero.

Signed-off-by: Wei Yang <[e-mail]>
Reviewed-by: Sean Christopherson <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/include/asm/kvm_host.h

···
 				   gfn_t gfn_offset, unsigned long mask);
 void kvm_mmu_zap_all(struct kvm *kvm);
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen);
-unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
+unsigned int kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
 
 int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3);

arch/x86/kvm/mmu.c

···
 /*
  * Calculate mmu pages needed for kvm.
  */
-unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
+unsigned int kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm)
 {
 	unsigned int nr_mmu_pages;
 	unsigned int  nr_pages = 0;

arch/x86/kvm/x86.c

···
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	int nr_mmu_pages = 0;
-
 	if (!kvm->arch.n_requested_mmu_pages)
-		nr_mmu_pages = kvm_mmu_calculate_mmu_pages(kvm);
-
-	if (nr_mmu_pages)
-		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
+		kvm_mmu_change_mmu_pages(kvm,
+				kvm_mmu_calculate_default_mmu_pages(kvm));
 
 	/*
 	 * Dirty logging tracks sptes in 4k granularity, meaning that large