md/raid10: fix bug when raid10 recovery fails to recover a block.

commit e875ecea
    md/raid10 record bad blocks as needed during recovery.

added code to the "cannot recover this block" path to record a bad
block rather than fail the whole recovery.
Unfortunately this new case was placed *after* r10bio was freed rather
than *before*, yet it still uses r10bio.
This is will crash with a null dereference.

So move the freeing of r10bio down where it is safe.

Cc: stable@vger.kernel.org (v3.1+)
Fixes: e875ecea
Reported-by: Damian Nowak <spam@nowaker.net>
URL: https://bugzilla.kernel.org/show_bug.cgi?id=68181


Signed-off-by: NeilBrown <neilb@suse.de>