Avoid compiler warning about size comparison

GCC warns about comparing uint8_t to a size that may be >255.

Strangely, casting the uint8_t to a size_t in the comparison expression
doesn't avoid the warning. So change the type of the variable.

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

library/ssl_tls12_client.c

@@ -1727,7 +1727,7 @@ static int ssl_parse_server_ecdh_params(mbedtls_ssl_context *ssl,
                                         unsigned char *end)
 {
     uint16_t tls_id;
-    uint8_t ecpoint_len;
+    size_t ecpoint_len;
     mbedtls_ssl_handshake_params *handshake = ssl->handshake;
     psa_key_type_t key_type = PSA_KEY_TYPE_NONE;
     size_t ec_bits = 0;