Fix compiler warnings

Fix multiple compiler warnings including:
* Unused variables
* Missing header include
* Format string

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: I94c8f95720a74835a2aacb7526fd94fc8ea005ce
diff --git a/deployments/sfs-demo/common/sfs_demo_sp.c b/deployments/sfs-demo/common/sfs_demo_sp.c
index cf3d795..ee0c93f 100644
--- a/deployments/sfs-demo/common/sfs_demo_sp.c
+++ b/deployments/sfs-demo/common/sfs_demo_sp.c
@@ -9,6 +9,7 @@
 #include "service/secure_storage/backend/secure_storage_client/secure_storage_client.h"
 #include "psa/internal_trusted_storage.h"
 #include "sp_api.h"
+#include "sp_discovery.h"
 #include "sp_messaging.h"
 #include "sp_rxtx.h"
 #include "trace.h"