Update documentation of mbedtls_pk_setup_opaque()

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/pk.c b/library/pk.c
index 9b16eca..0f465cd 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -703,7 +703,7 @@
  * Load the key to a PSA key slot,
  * then turn the PK context into a wrapper for that key slot.
  *
- * Currently only works for EC private keys.
+ * Currently only works for EC & RSA private keys.
  */
 int mbedtls_pk_wrap_as_opaque( mbedtls_pk_context *pk,
                                mbedtls_svc_key_id_t *key,