md/raid1/10: reset bio allocated from mempool

Data allocated from mempool doesn't always get initialized, this happens when
the data is reused instead of fresh allocation. In the raid1/10 case, we must
reinitialize the bios.

Reported-by: Jonathan G. Underwood <jonathan.underwood@gmail.com>
Fixes: f0250618(md: raid10: don't use bio's vec table to manage resync pages)
Fixes: 98d30c58(md: raid1: don't use bio's vec table to manage resync pages)
Cc: stable@vger.kernel.org (4.12+)
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Shaohua Li <shli@fb.com>