xen/console: Fix build when CONFIG_DEBUG_TRACE=y

Commit b5e6e1ee8d "xen/console: Don't treat NUL character as the end
of the buffer" extended sercon_puts to take the number of character
to print in argument.

Sadly, a couple of couple of the callers in debugtrace_dump_worker()
were not converted. This result to a build failure when enabling
CONFIG_DEBUG_TRACE.

Spotted by Travis using randconfig
Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/drivers/char/console.c

@@ -1185,11 +1185,13 @@ static void debugtrace_dump_worker(void)
 
     /* Print oldest portion of the ring. */
     ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
-    sercon_puts(&debugtrace_buf[debugtrace_prd]);
+    if ( debugtrace_buf[debugtrace_prd] != '\0' )
+        sercon_puts(&debugtrace_buf[debugtrace_prd],
+                    strlen(&debugtrace_buf[debugtrace_prd]));
 
     /* Print youngest portion of the ring. */
     debugtrace_buf[debugtrace_prd] = '\0';
-    sercon_puts(&debugtrace_buf[0]);
+    sercon_puts(&debugtrace_buf[0], debugtrace_prd);
 
     memset(debugtrace_buf, '\0', debugtrace_bytes);