md/raid10: fix leak of 'r10bio->remaining' for recovery

In the Linux kernel, the following vulnerability has been resolved:

md/raid10: fix leak of 'r10bio->remaining' for recovery

raid10_sync_request() will add 'r10bio->remaining' for both rdev and

replacement rdev. However, if the read io fails, recovery_request_write()

returns without issuing the write io, in this case, end_sync_request()

is only called once and 'remaining' is leaked, cause an io hang.

Fix the problem by decreasing 'remaining' according to if 'bio' and

'repl_bio' is valid.