Fix OS calling PSCI directly in the nwd capsule install diagram

source/uml/bl33_nwd_capsule_install.txt

@@ -8,8 +8,11 @@ participant OS #7773cf
 activate OS
 OS -> OS : set ACCEPTANCE_REQUEST on intended capsules
 OS -> UEFI: Schedule CapsuleUpdate() on reboot
-OS -> TFA: PSCI_SYSTEM_RESET
+OS -> UEFI ++: Call ResetSystem()
+UEFI -> TFA: PSCI_SYSTEM_RESET
+deactivate UEFI
 TFA -> UEFI ++:
 UEFI -> FWU: Perform FW update
+
 UEFI -> TFA: PSCI_SYSTEM_RESET
 @enduml