Make handshake hashing functions return int

There are three family of functions: update_checksum, calc_verify,
calc_finished, that perform hashing operations and were returning void
so far. This is not correct, as hashing functions can return errors (for
example, on hardware failure when accelerated). Change them to return
int.

This commit just changes the types: for now the functions always return
0, and their return value is not checked; this will be fixed in the
next few commits.

There is a related function in TLS 1.3,
mbedtls_ssl_reset_transcript_for_hrr, which also handles hashes, and
already returns int but does not correctly check for errors from hashing
functions so far, it will also be handled in the next few commits.

There's a special case with handshake_params_init: _init functions
should return void, so we'll need to split out the part that can return
errors, see the next commit.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 2668a05..bffbef2 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -705,9 +705,9 @@
 
     mbedtls_ssl_ciphersuite_t const *ciphersuite_info;
 
-    void (*update_checksum)(mbedtls_ssl_context *, const unsigned char *, size_t);
-    void (*calc_verify)(const mbedtls_ssl_context *, unsigned char *, size_t *);
-    void (*calc_finished)(mbedtls_ssl_context *, unsigned char *, int);
+    int (*update_checksum)(mbedtls_ssl_context *, const unsigned char *, size_t);
+    int (*calc_verify)(const mbedtls_ssl_context *, unsigned char *, size_t *);
+    int (*calc_finished)(mbedtls_ssl_context *, unsigned char *, int);
     mbedtls_ssl_tls_prf_cb *tls_prf;
 
     /*
@@ -1317,7 +1317,7 @@
 MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_send_fatal_handshake_failure(mbedtls_ssl_context *ssl);
 
-void mbedtls_ssl_reset_checksum(mbedtls_ssl_context *ssl);
+int mbedtls_ssl_reset_checksum(mbedtls_ssl_context *ssl);
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 MBEDTLS_CHECK_RETURN_CRITICAL