The code responsible for reading the version of the mirror bbt was
incorrectly using the descriptor of the main bbt.

Pass the mirror bbt descriptor to 'scan_read_raw' when reading the
version of the mirror bbt.
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable@vger.kernel.org [v2.6.37+]
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>