Initialize xferStartTime for StoreData timings

Initialize xferStartTime for StoreData timings

In the reorganization of fetch and store procs, the initialization of
the transfer start time for a store was lost, leading to meaningless
statistics from the uninitialized variable.  Initialize the transfer
time at the start of transferring each chunk and move the variable into
the for loop.

Reviewed-on: http://gerrit.openafs.org/340
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>