LU-15522 util: make readline() static

LU-15522 util: make readline() static

In libcfs/libcfs/util/parser.c make readline() static to avoid
conflicting with the real readline().

Test-Parameters: trivial
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I4b90fd5d22c9fd5d193f5d18588afd3d97ca591c
Reviewed-on: https://review.whamcloud.com/46465
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>