Build: Correct header location for PSA tests

Change from looking for generated partition headers in the
psa-arch-tests dir to in the <build_dir>/generated dir

Change-Id: Id4ba56078d32d69a609965b7298ec70d7851fc88
Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/app/CMakeLists.txt b/app/CMakeLists.txt
index e89bf66..9770d20 100644
--- a/app/CMakeLists.txt
+++ b/app/CMakeLists.txt
@@ -36,7 +36,7 @@
 
     if(NOT PSA_INCLUDE_PATHS)
         set(PSA_INCLUDE_PATHS ${CMAKE_SOURCE_DIR}/interface/include/
-                              ${PSA_ARCH_TESTS_PATH}/api-tests/platform/manifests/
+                              ${CMAKE_BINARY_DIR}/generated/api-tests/platform/manifests/
                               ${CMAKE_BINARY_DIR}/generated/interface/include
         )
     endif()