LU-13723 lustre: Convert ERR_PTR(PTR_ERR()) to ERR_CAST()

LU-13723 lustre: Convert ERR_PTR(PTR_ERR()) to ERR_CAST()

This patch converts ERR_PTR(PTR_ERR()) to ERR_CAST()
This fixes warning thrown by coccinelle

It also updates contrib/scripts/spelling.txt to catch
any future misuse of ERR_PTR(PTR_ERR())

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I2214f46c08e5295dd139e7b4b245881cd9f6495a
Reviewed-on: https://review.whamcloud.com/39204
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>