doc: Fixup some SMCCC links

This is a fixup for patch 3ba55a3c5fa260c9218be1adff8f39fc2a568d68
("docs: Update SMCCC doc, other changes for release"), where some
links names got changed but their references didn't.

Change-Id: I980d04dde338f3539a2ec1ae2e807440587b1cf5
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index 7d99d86..b336b38 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -544,7 +544,7 @@
 exception vectors implement more elaborate support for handling SMCs since this
 is the only mechanism to access the runtime services implemented by BL31 (PSCI
 for example). BL31 checks each SMC for validity as specified by the
-`SMC Calling Convention PDD`_ before passing control to the required SMC
+`SMC Calling Convention`_ before passing control to the required SMC
 handler routine.
 
 BL31 programs the ``CNTFRQ_EL0`` register with the clock frequency of the system
@@ -2711,7 +2711,7 @@
 
 -  `Power State Coordination Interface PDD`_
 
--  `SMC Calling Convention PDD`_
+-  `SMC Calling Convention`_
 
 -  :ref:`Interrupt Management Framework`