cpukit/libblock/*: Address unused parameter warnings

Add "(void) param;" annotation to address unused parameter warnings.
Found with GCC's warning -Wunused-paramter.

cpukit/libblock/src/bdbuf.c

@@ -2949,6 +2949,8 @@ rtems_bdbuf_set_block_size (rtems_disk_device *dd,
 static rtems_task
 rtems_bdbuf_read_ahead_task (rtems_task_argument arg)
 {
+  (void) arg;
+
   rtems_chain_control *chain = &bdbuf_cache.read_ahead_chain;
 
   while (bdbuf_cache.read_ahead_enabled)

cpukit/libblock/src/diskdevs.c

@@ -217,6 +217,10 @@ static int null_handler(
   void *argp
 )
 {
+  (void) dd;
+  (void) req;
+  (void) argp;
+
   return -1;
 }