LU-13891 utils: fix memory leak in llapi_ladvise()

LU-13891 utils: fix memory leak in llapi_ladvise()

A buffer allocated in llapi_ladvise() for ioctl() is never
released. This patch ensures the buffer is properly freed.

Fixes: e14246641c04 ("LU-4931 ladvise: Add feature of giving file access advices")
Signed-off-by: Jean-Yves VET <jyvet@ddn.com>
Change-Id: I0761e161074ae3029218473ec951670fdbbd33bd
Reviewed-on: https://review.whamcloud.com/39610
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>