LU-9679 osc: convert while to for in get_write_extents()

LU-9679 osc: convert while to for in get_write_extents()

This 'while' loop is really a 'for' loop in disguise.
So change it to 'for'.

Linux-Commit: d3ba9dc5cc66 ("lustre: osc_cache: convert while to for
	in get_write_extents()")

Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: Ifd4295cbdad400d2c49d83e0c54ddd0e4c5ae548
Reviewed-on: https://review.whamcloud.com/37608
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <farr0186@gmail.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>