LU-15198 llite: Use percpu_env for tiny_write_end

LU-15198 llite: Use percpu_env for tiny_write_end

The percpu cl_env can be used in situations where it is
known the caller will not be rescheduled.  This is true for
ll_tiny_write_end, and switching to the percpu env gives
a performance improvement of a little over 7%.

dd, write size 8 bytes
Before:
14.3 MiB/s
After:
15.4 MiB/s

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Iadeabf145416d80f6cb063ccdc8bccb4b4b214a1
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/45477
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Aurelien Degremont <adegremont@nvidia.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>