bcache: Fix an error code in bch_dump_read()

The copy_to_user() function returns the number of bytes remaining to be
copied, but the intention here was to return -EFAULT if the copy fails.

Fixes: cafe5635 ("bcache: A block layer cache")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/md/bcache/debug.c

@@ -178,10 +178,9 @@ static ssize_t bch_dump_read(struct file *file, char __user *buf,
 	while (size) {
 		struct keybuf_key *w;
 		unsigned int bytes = min(i->bytes, size);
-		int err = copy_to_user(buf, i->buf, bytes);
 
-		if (err)
-			return err;
+		if (copy_to_user(buf, i->buf, bytes))
+			return -EFAULT;
 
 		ret	 += bytes;
 		buf	 += bytes;