Fix typo in comment
Change from from lower case to upper case in XXX_ALT
comment in `MBEDTLS_ECP_RESTARTABLE` description.
*
* \note This option only works with the default software implementation of
* elliptic curve functionality. It is incompatible with
- * MBEDTLS_ECP_ALT, MBEDTLS_ECDH_xxx_ALT and MBEDTLS_ECDSA_xxx_ALT.
+ * MBEDTLS_ECP_ALT, MBEDTLS_ECDH_XXX_ALT and MBEDTLS_ECDSA_XXX_ALT.
*/
//#define MBEDTLS_ECP_RESTARTABLE
