KVM: x86: Make enum conversion explicit in kvm_pdptr_read()

The type 'enum kvm_reg_ex' is an extension of 'enum kvm_reg', however
the extension is only semantical and the compiler doesn't know about the
relationship between the two types. In kvm_pdptr_read() a value of the
extended type is passed to kvm_x86_ops->cache_reg(), which expects a
value of the base type. Clang raises the following warning about the
type mismatch:

arch/x86/kvm/kvm_cache_regs.h:44:32: warning: implicit conversion from
  enumeration type 'enum kvm_reg_ex' to different enumeration type
  'enum kvm_reg' [-Wenum-conversion]
    kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);

Cast VCPU_EXREG_PDPTR to 'enum kvm_reg' to make the compiler happy.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/kvm_cache_regs.h

@@ -41,7 +41,7 @@ static inline u64 kvm_pdptr_read(struct kvm_vcpu *vcpu, int index)
 
 	if (!test_bit(VCPU_EXREG_PDPTR,
 		      (unsigned long *)&vcpu->arch.regs_avail))
-		kvm_x86_ops->cache_reg(vcpu, VCPU_EXREG_PDPTR);
+		kvm_x86_ops->cache_reg(vcpu, (enum kvm_reg)VCPU_EXREG_PDPTR);
 
 	return vcpu->arch.walk_mmu->pdptrs[index];
 }