Core: fix preprocessor directive

Changes '#if TFM_PSA_API' to '#ifdef TFM_PSA_API'.

Change-Id: I2211977a84f1a079dd35990c13f941f82620d543
Signed-off-by: Robert Rostohar <Robert.Rostohar@arm.com>
diff --git a/secure_fw/spm/spm_db.h b/secure_fw/spm/spm_db.h
index 8a907a4..34e9693 100644
--- a/secure_fw/spm/spm_db.h
+++ b/secure_fw/spm/spm_db.h
@@ -48,7 +48,7 @@
     struct spm_partition_runtime_data_t runtime_data;
     const struct spm_partition_static_data_t *static_data;
     const struct tfm_spm_partition_platform_data_t *platform_data;
-#if TFM_PSA_API
+#ifdef TFM_PSA_API
     const struct tfm_spm_partition_memory_data_t *memory_data;
 #endif
 };