Update documentation

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index db0bfac..386ec42 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -496,7 +496,9 @@
  *
  * \note            If type is MBEDTLS_PK_RSASSA_PSS, then options must point
  *                  to a mbedtls_pk_rsassa_pss_options structure,
- *                  otherwise it must be NULL.
+ *                  otherwise it must be NULL. Note that if
+ *                  #MBEDTLS_USE_PSA_CRYPTO is defined, the salt length is not
+ *                  verified as PSA_ALG_RSA_PSS_ANY_SALT is used.
  */
 int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
                    mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,