Fix long-standing bug in error code description

MBEDTLS_ERR_ASN1_INVALID_DATA is documented as "not used", but it has
been used since the PolarSSL days.

Author: gilles-peskine-arm

include/mbedtls/asn1.h

@@ -52,7 +52,7 @@
 #define MBEDTLS_ERR_ASN1_UNEXPECTED_TAG                   -0x0062  /**< ASN1 tag was of an unexpected value. */
 #define MBEDTLS_ERR_ASN1_INVALID_LENGTH                   -0x0064  /**< Error when trying to determine the length or invalid length. */
 #define MBEDTLS_ERR_ASN1_LENGTH_MISMATCH                  -0x0066  /**< Actual length differs from expected length. */
-#define MBEDTLS_ERR_ASN1_INVALID_DATA                     -0x0068  /**< Data is invalid. (not used) */
+#define MBEDTLS_ERR_ASN1_INVALID_DATA                     -0x0068  /**< Data is invalid. */
 #define MBEDTLS_ERR_ASN1_ALLOC_FAILED                     -0x006A  /**< Memory allocation failed */
 #define MBEDTLS_ERR_ASN1_BUF_TOO_SMALL                    -0x006C  /**< Buffer too small when writing ASN.1 data structure. */