Update gpcp.xml

Correct a typo? The latest error is vague.

Author: zjbdragon

input/gpcp.xml

@@ -2427,7 +2427,7 @@
 					key may be found while in use and between uses. Cryptographic material that is infeasible to
 					destroy shall also be identified accompanied with a justification or explanation. Keys
 					related to the operation of or under the protection of an FDE may be subject to requirements
-					enumerated in the FDE cPP.
+					enumerated in the FDE cPPs.
 				</note>
 			</f-element>
 			<f-element id="fcs-ckm-6e2">