mtd: mtdblock: remove the needless mtdblks_lock

The global lock mtdblks_lock was used to protect the original mtdblks
array to avoid race conditions. As the mtdblks array was already gone,
but the mtdblks_lock is left, and it causes latency when open/release dev.
So we need to remove it here.

Signed-off-by: Gu Zheng <[e-mail]>
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/mtdblock.c

···
 	enum { STATE_EMPTY, STATE_CLEAN, STATE_DIRTY } cache_state;
 };
 
-static DEFINE_MUTEX(mtdblks_lock);
-
 /*
  * Cache stuff...
  *
···
 
 	pr_debug("mtdblock_open\n");
 
-	mutex_lock(&mtdblks_lock);
 	if (mtdblk->count) {
 		mtdblk->count++;
-		mutex_unlock(&mtdblks_lock);
 		return 0;
 	}
 
···
 		mtdblk->cache_data = NULL;
 	}
 
-	mutex_unlock(&mtdblks_lock);
-
 	pr_debug("ok\n");
 
 	return 0;
···
 	struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
 
 	pr_debug("mtdblock_release\n");
-
-	mutex_lock(&mtdblks_lock);
 
 	mutex_lock(&mtdblk->cache_mutex);
 	write_cached_data(mtdblk);
···
 			mtd_sync(mbd->mtd);
 		vfree(mtdblk->cache_data);
 	}
-
-	mutex_unlock(&mtdblks_lock);
 
 	pr_debug("ok\n");
 }