Move MBEDTLS_ERR_xxx Doxygen comments before the definition

Now that descriptions of error codes no longer have to be on the same line
for the sake of generate_errors.pl, move them to their own line before the
definition. This aligns them with what we do for other definitions, and
means that we no longer need to have very long lines containing both the C
definition and the comment.

```
perl -i -pe 's~^(#define +MBEDTLS_ERR_\w+ +-\w+) */\*[*!]<(.*)\*/~/**$2*/\n$1~' include/mbedtls/*.h
```

This commit does not change the output of generate_errors.pl.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/chachapoly.h b/include/mbedtls/chachapoly.h
index 1007f95..c4ec7b5 100644
--- a/include/mbedtls/chachapoly.h
+++ b/include/mbedtls/chachapoly.h
@@ -41,8 +41,10 @@
 /* for shared error codes */
 #include "mbedtls/poly1305.h"
 
-#define MBEDTLS_ERR_CHACHAPOLY_BAD_STATE            -0x0054 /**< The requested operation is not permitted in the current state. */
-#define MBEDTLS_ERR_CHACHAPOLY_AUTH_FAILED          -0x0056 /**< Authenticated decryption failed: data was not authentic. */
+/** The requested operation is not permitted in the current state. */
+#define MBEDTLS_ERR_CHACHAPOLY_BAD_STATE            -0x0054
+/** Authenticated decryption failed: data was not authentic. */
+#define MBEDTLS_ERR_CHACHAPOLY_AUTH_FAILED          -0x0056
 
 #ifdef __cplusplus
 extern "C" {