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>
diff --git a/include/psa/crypto_compat.h b/include/psa/crypto_compat.h
index 7ae6cbb..5cb225b 100644
--- a/include/psa/crypto_compat.h
+++ b/include/psa/crypto_compat.h
@@ -470,11 +470,11 @@
  *         permission to access it. Note that this specification does not
  *         define any way to create such a key, but it may be possible
  *         through implementation-specific means.
- * \retval #PSA_ERROR_COMMUNICATION_FAILURE
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
- * \retval #PSA_ERROR_STORAGE_FAILURE
- * \retval #PSA_ERROR_DATA_INVALID
- * \retval #PSA_ERROR_DATA_CORRUPT
+ * \retval #PSA_ERROR_COMMUNICATION_FAILURE \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
+ * \retval #PSA_ERROR_STORAGE_FAILURE \emptydescription
+ * \retval #PSA_ERROR_DATA_INVALID \emptydescription
+ * \retval #PSA_ERROR_DATA_CORRUPT \emptydescription
  * \retval #PSA_ERROR_BAD_STATE
  *         The library has not been previously initialized by psa_crypto_init().
  *         It is implementation-dependent whether a failure to initialize
@@ -514,8 +514,8 @@
  *         \p handle was a valid handle or \c 0. It is now closed.
  * \retval #PSA_ERROR_INVALID_HANDLE
  *         \p handle is not a valid handle nor \c 0.
- * \retval #PSA_ERROR_COMMUNICATION_FAILURE
- * \retval #PSA_ERROR_CORRUPTION_DETECTED
+ * \retval #PSA_ERROR_COMMUNICATION_FAILURE \emptydescription
+ * \retval #PSA_ERROR_CORRUPTION_DETECTED \emptydescription
  * \retval #PSA_ERROR_BAD_STATE
  *         The library has not been previously initialized by psa_crypto_init().
  *         It is implementation-dependent whether a failure to initialize