md/raid10: make sync_request_write() call bio_copy_data()

md/raid10: make sync_request_write() call bio_copy_data()

Refactor sync_request_write() of md/raid10 to use bio_copy_data()
instead of open coding bio_vec iterations.

Cc: Christoph Hellwig <[email protected]>
Cc: Neil Brown <[email protected]>
Cc: [email protected]
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: NeilBrown <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>
[dpark: add more description in commit message]
Signed-off-by: Dongsu Park <[email protected]>
Signed-off-by: Ming Lin <[email protected]>
Signed-off-by: NeilBrown <[email protected]>