Add ftruncate into file operation calls

- Add truncate into file_operations
- Move truncate to be common for mountpt_operations and file_operations
- Modify all drivers to initialize the operations struct accordingly

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

drivers/sensors/hc_sr04.c

@@ -90,6 +90,7 @@ static const struct file_operations g_hcsr04ops =
   hcsr04_write,  /* write */
   NULL,          /* seek */
   hcsr04_ioctl,  /* ioctl */
+  NULL,          /* truncate */
   hcsr04_poll    /* poll */
 #ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
   , NULL         /* unlink */