pk: fix position for mbedtls_platform_zeroize

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/pk.c b/library/pk.c
index 04c5e40..4e2f218 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -904,12 +904,11 @@
 
         /* import private key into PSA */
         status = psa_import_key(&attributes, d, d_len, key);
+        mbedtls_platform_zeroize(d, sizeof(d));
         if (status != PSA_SUCCESS) {
             return PSA_PK_TO_MBEDTLS_ERR(status);
         }
 
-        mbedtls_platform_zeroize(d, sizeof(d));
-
         /* make PK context wrap the key slot */
         mbedtls_pk_free(pk);
         mbedtls_pk_init(pk);