Remove the unnecessary NULL fields in global instance definition of file_operations

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

drivers/loop/loop.c

@@ -57,10 +57,6 @@ static const struct file_operations g_loop_fops =
   loop_write,    /* write */
   NULL,          /* seek */
   loop_ioctl,    /* ioctl */
-  NULL           /* poll */
-#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
-  , NULL         /* unlink */
-#endif
 };
 
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