LU-14587 ptlrpc: remove LASSERT in nrs_polices proc handler

LU-14587 ptlrpc: remove LASSERT in nrs_polices proc handler

It's not necessary to LASSERT() in nrs_polices proc handler.
CERROR() and returning error is good enough.

Lustre-change: https://review.whamcloud.com/45200
Lustre-commit: 9997f94d4b6ee335d2bf86f94bd43464d5b8f061

Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: trivial
Change-Id: I09f06dc4ab90e49b2df66a9b47a74678c64cdd2f
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-on: https://review.whamcloud.com/46769
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>