Remove a kludge for the output size of mbedtls_sha512_finish_ret

Remove a kludge to avoid a warning in GCC 11 when calling
mbedtls_sha512_finish_ret with a 48-byte output buffer. This is correct
since we're calculating SHA-384. When mbedtls_sha512_finish_ret's output
parameter was declared as a 64-byte array, GCC 11 -Wstringop-overflow
emitted a well-meaning, but inaccurate buffer overflow warning, which we
tried to work around (successfully with beta releases but unsuccessfully
with GCC 11.1.0 as released). Now that the output parameter is declared as a
pointer, no workaround is necessary.

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

library/ssl_tls.c

@@ -2897,8 +2897,6 @@ static void ssl_calc_finished_tls_sha256(
 
 #if defined(MBEDTLS_SHA512_C)
 
-typedef int (*finish_sha384_t)(mbedtls_sha512_context*, unsigned char*);
-
 static void ssl_calc_finished_tls_sha384(
                 mbedtls_ssl_context *ssl, unsigned char *buf, int from )
 {
@@ -2957,13 +2955,7 @@ static void ssl_calc_finished_tls_sha384(
     MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha512 state", (unsigned char *)
                    sha512.state, sizeof( sha512.state ) );
 #endif
-    /*
+    mbedtls_sha512_finish_ret( &sha512, padbuf );
-     * For SHA-384, we can save 16 bytes by keeping padbuf 48 bytes long.
-     * However, to avoid stringop-overflow warning in gcc, we have to cast
-     * mbedtls_sha512_finish_ret().
-     */
-    finish_sha384_t finish = (finish_sha384_t)mbedtls_sha512_finish_ret;
-    finish( &sha512, padbuf );
 
     mbedtls_sha512_free( &sha512 );
 #endif