drivers/sensors/apds9960.c: Fix use after free

Memory pointed by priv may be used (in line 1289) after it is
freed in line 1283.
Fix by adding the missing return statement in error handling.

Signed-off-by: Mingjie Shen <shen497@purdue.edu>

drivers/sensors/apds9960.c

@@ -1281,6 +1281,7 @@ int apds9960_register(FAR const char *devpath,
     {
       snerr("ERROR: Failed to register driver: %d\n", ret);
       kmm_free(priv);
+      return ret;
     }
 
   /* Attach to the interrupt */