LU-6142 contrib: fix typo in spelling.txt file

LU-6142 contrib: fix typo in spelling.txt file

Any patch that mentions cfs_time_seconds() gets a
weird warning from checkpatch due to this typo.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: Ifeb54992c991f7f6cbcd0a9fd5aca5158adb2a4f
Reviewed-on: https://review.whamcloud.com/35965
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>