Fixes some issues found by the PX4 team using Coverity. From Pavel Krienko

nuttx/drivers/pipes/pipe.c

@@ -275,7 +275,10 @@ errout_with_wrfd:
 errout_with_driver:
   unregister_driver(devname);
 errout_with_dev:
-  pipecommon_freedev(dev);
+  if (dev)
+    {
+      pipecommon_freedev(dev);
+    }
 errout_with_pipe:
   pipe_free(pipeno);
 errout:

nuttx/drivers/usbdev/cdcacm.c

@@ -1205,14 +1205,15 @@ static void cdcacm_unbind(FAR struct usbdevclass_driver_s *driver,
               priv->nwrq--;     /* Number of write requests queued */
             }
         }
+
       DEBUGASSERT(priv->nwrq == 0);
       irqrestore(flags);
+
+      /* Clear out all data in the circular buffer */
+
+      priv->serdev.xmit.head = 0;
+      priv->serdev.xmit.tail = 0;
     }
-
-  /* Clear out all data in the circular buffer */
-
-  priv->serdev.xmit.head = 0;
-  priv->serdev.xmit.tail = 0;
 }
 
 /****************************************************************************

nuttx/mm/mm_gran/mm_granalloc.c

@@ -245,9 +245,10 @@ static inline FAR void *gran_common_alloc(FAR struct gran_s *priv, size_t size)
               bitidx += shift;
             }
         }
+
+      gran_leave_critical(priv);
     }
 
-  gran_leave_critical(priv);
   return NULL;
 }