LU-6142 osd-zfs: convert container_of0() to container_of()

LU-6142 osd-zfs: convert container_of0() to container_of()

Every use of container_of0() in osd-zfs can safely use container_of()
instead.  Doing so makes the intent of the code clearer.

In most cases, the pointer returned is later dereferenced without any
subsequent checks.  In a few cases (e.g.  in osd_internal.h), the
pointer passed in is dereferenced before the container_of() call.
These patterns assure us that the pointer in valid (not NULL or an
ERR_PTR), so container_of() is the correct interface to use.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I3f6d35c8b5beee09561e78c5eb20bb89d322590b
Reviewed-on: https://review.whamcloud.com/38379
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>