Fix issue #40

Signed-off-by: Miguel Angel Reina Ortega <miguelangel.reinaortega@etsi.org>

CDT-AE.xsd

@@ -79,7 +79,7 @@ oneM2M EXPRESSLY ADVISES ANY AND ALL USE OF OR RELIANCE UPON THIS INFORMATION PR
 								<xs:element ref="m2m:group" />
 								<xs:element ref="m2m:accessControlPolicy" />
 								<xs:element ref="m2m:subscription" />
-								<xs:element ref="m2m:pollingChannel" />
+								<xs:element ref="m2m:pollingChannel" maxOccurs="1"/>
 								<xs:element ref="m2m:semanticDescriptor" />
 								<xs:element ref="m2m:timeSeries" />
 								<xs:element ref="m2m:sg_flexContainerResource" />