LU-9679 osc: convert a while loop to for

LU-9679 osc: convert a while loop to for

This loop uses 'continue' in several places,
and each one is proceeded by
   ext = next_extent(ext)
which also appears at the end.
This is exactly the pattern that a 'for' loop
simplifies.  So change to a for loop.

Linux-Commit 9083b739197b ("lustre: osc: convert a while loop to for")

Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: Ie622690134f9b3ee829255bcf997d06289abd6e6
Reviewed-on: https://review.whamcloud.com/37606
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>