Give a constant a name in test function

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 40ab19d..36023dd 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -3475,6 +3475,7 @@
     unsigned char add_data[13];
     unsigned char mac[MBEDTLS_MD_MAX_SIZE];
     int exp_ret;
+    const unsigned char pad_max_len = 255; /* Per the standard */
 
     mbedtls_ssl_init( &ssl );
     mbedtls_ssl_transform_init( &t0 );
@@ -3492,7 +3493,7 @@
     if( padlen == block_size )
         padlen = 0;
     if( pad_long )
-        padlen += block_size * ( ( 255 - padlen ) / block_size );
+        padlen += block_size * ( ( pad_max_len - padlen ) / block_size );
 
     /* Prepare a buffer for record data */
     buflen = block_size
@@ -3606,7 +3607,7 @@
      * (Start the loop with correct padding, just to double-check that record
      * saving did work, and that we're overwriting the correct bytes.)
      */
-    for( i = padlen; i <= 255; i++ )
+    for( i = padlen; i <= pad_max_len; i++ )
     {
         test_set_step( i );