LU-6142 libcfs: discard cfs_firststr

LU-6142 libcfs: discard cfs_firststr

The effect of cfs_firststr() can easily achieved with
skip_space() and strsep().

So use that instead.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Idcf8aa50b6aad052f7ee5341ce6d635495aa4990
Reviewed-on: https://review.whamcloud.com/40860
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>