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.

Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: trivial
Change-Id: I09f06dc4ab90e49b2df66a9b47a74678c64cdd2f
Reviewed-on: https://review.whamcloud.com/45200
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>