LU-12705 utils: cleanup unnecessary typecasting

LU-12705 utils: cleanup unnecessary typecasting

There're a bunch of variables typeecasted in utils/lfs.c where
they are not needed, so cleanup them here.

Lustre-change: https://review.whamcloud.com/36224
Lustre-commit: d8135ad2fbe58a0fbe6984584816338542901c5c

Change-Id: I6c944f18137fd1ff1162d9b6567c9328dfa185eb
Test-Parameters: trivial
Signed-off-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36313
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>