Documentation improvements

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/psa_crypto_rsa.h b/library/psa_crypto_rsa.h
index 134844b..1a78000 100644
--- a/library/psa_crypto_rsa.h
+++ b/library/psa_crypto_rsa.h
@@ -106,7 +106,7 @@
  * \brief Generate an RSA key.
  *
  * \param[in]  attributes         The attributes for the RSA key to generate.
- * \param[in]  custom             The public exponent to use.
+ * \param[in]  custom_data        The public exponent to use.
  *                                This can be a null pointer if
  *                                \c params_data_length is 0.
  * \param custom_data_length      Length of \p custom_data in bytes.
@@ -126,7 +126,7 @@
  */
 psa_status_t mbedtls_psa_rsa_generate_key(
     const psa_key_attributes_t *attributes,
-    const uint8_t *custom, size_t custom_data_length,
+    const uint8_t *custom_data, size_t custom_data_length,
     uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length);
 
 /** Sign an already-calculated hash with an RSA private key.