Make \retval commands non-empty

Pacify Clang >=15 which complained:
```
include/psa/crypto.h:91:23: error: empty paragraph passed to '\retval' command [-Werror,-Wdocumentation]
 * \retval #PSA_SUCCESS
   ~~~~~~~~~~~~~~~~~~~^
```

This commit performs the following systematic replacement:
```
perl -i -0777 -p -e 's/([\\@])(retval +\S+)\n(?! *\*? *([^\n \\*\/]|\\[cp]\b))/$1$2 ${1}emptydescription\n/g' $(git ls-files '*.[hc]' '*.function' '*.jinja')
```
i.e. add an `\emptydescription` argument to `\retval` commands (or
`@retval`, which we don't normally used) that are followed by a single word,
unless the next line looks like it contains text which would be the
description.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/data_files/driver_templates/psa_crypto_driver_wrappers.c.jinja

@@ -441,9 +441,9 @@ psa_status_t psa_driver_wrapper_verify_hash(
  * \param[in] data_length       The input data length.
  * \param[out] key_buffer_size  Minimum buffer size to contain the key material.
  *
- * \retval #PSA_SUCCESS
- * \retval #PSA_ERROR_INVALID_ARGUMENT
- * \retval #PSA_ERROR_NOT_SUPPORTED
+ * \retval #PSA_SUCCESS \emptydescription
+ * \retval #PSA_ERROR_INVALID_ARGUMENT \emptydescription
+ * \retval #PSA_ERROR_NOT_SUPPORTED \emptydescription
  */
 psa_status_t psa_driver_wrapper_get_key_buffer_size_from_key_data(
     const psa_key_attributes_t *attributes,