Spin the twiddle in dosfs to give visual feedback for disk I/O on

FAT filesystems as is done for other filesystems in the loader.

MFC after:	1 week

lib/libstand/dosfs.c

@@ -786,7 +786,8 @@ static int
 ioget(struct open_file *fd, u_int lsec, void *buf, u_int nsec)
 {
     int	err;
-    
+
+    twiddle(1);
     if ((err = (fd->f_dev->dv_strategy)(fd->f_devdata, F_READ, lsec, 
 					secbyt(nsec), buf, NULL)))
 	return(err);