mtd: block: use a simple bool to track open for write

Instead of propagating the fmode_t, just use a bool to track if a mtd
block device was opened for writing.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Acked-by: Christian Brauner <[e-mail]>
Acked-by: Richard Weinberger <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/mtd/mtd_blkdevs.c

···
 	ret = __get_mtd_device(dev->mtd);
 	if (ret)
 		goto error_release;
-	dev->file_mode = mode;
+	dev->writable = mode & FMODE_WRITE;
 
 unlock:
 	dev->open++;

drivers/mtd/mtdblock.c

···
 		 * It was the last usage. Free the cache, but only sync if
 		 * opened for writing.
 		 */
-		if (mbd->file_mode & FMODE_WRITE)
+		if (mbd->writable)
 			mtd_sync(mbd->mtd);
 		vfree(mtdblk->cache_data);
 	}

include/linux/mtd/blktrans.h

···
 	struct blk_mq_tag_set *tag_set;
 	spinlock_t queue_lock;
 	void *priv;
-	fmode_t file_mode;
+	bool writable;
 };
 
 struct mtd_blktrans_ops {