A workaround to make sure /dev/mtd0 can be created

A workaround to make sure /dev/mtd0 can be created when memdisk is used.
This is due to sometimes "modprobe phram" can not successfully create /dev/mtd0.
Have to try several times.
Ref: https://gitlab.gnome.org/GNOME/gparted/issues/50#note_523831
     http://gparted-forum.surf4.info/viewtopic.php?pid=32784#p32784
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