mtd_blkdevs.c: do not export 'mtd_blktrans_ops'

The mtd_blktrans_ops is not defined in any of the headers and is indeed not used elsewhere in the kernel, so mark it as static to reduce the warnings from sparse

drivers/mtd/mtd_blkdevs.c:204:32: warning: symbol 'mtd_blktrans_ops' was not declared. Should it be static?

@@ -201,7 +201,7 @@ static int blktrans_ioctl(struct inode *
 	}
 }
 
-struct block_device_operations mtd_blktrans_ops = {
+static struct block_device_operations mtd_blktrans_ops = {
 	.owner		= THIS_MODULE,
 	.open		= blktrans_open,
 	.release	= blktrans_release,