LU-16043 osc: allow error for write on CL_FSYNC_DISCARD

LU-16043 osc: allow error for write on CL_FSYNC_DISCARD

If case of CL_FSYNC_DISCARD error is allowed for write of osc object.

Otherwise, the included test fails in rm with:
  (osc_page.c:174:osc_page_delete()) Trying to teardown failed: -16
  (osc_page.c:175:osc_page_delete()) ASSERTION( 0 ) failed:
  (osc_page.c:175:osc_page_delete()) LBUG

Test-Parameters: trivial testlist=sanity env=ONLY=907
HPE-bug-id: LUS-10410
Signed-off-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Change-Id: I0aae0dc470ba0371964e7643a6d84b19a1b4e106
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48032
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>