KVM: x86: Use DR7_GD macro instead of open coding check in emulator

Use DR7_GD in the emulator instead of open coding the check, and drop a
comically wrong comment.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-10-seanjc@google.comSigned-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -4166,8 +4166,7 @@ static int check_dr7_gd(struct x86_emulate_ctxt *ctxt)
 
 	ctxt->ops->get_dr(ctxt, 7, &dr7);
 
-	/* Check if DR7.Global_Enable is set */
-	return dr7 & (1 << 13);
+	return dr7 & DR7_GD;
 }
 
 static int check_dr_read(struct x86_emulate_ctxt *ctxt)