LU-6142 lustre: use init_wait(), not init_waitqueue_entry()

init_waitqueue_entry(foo, current)

is equivalent to

    init_wait(foo)

So use the shorter version - in lustre and libcfs.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I621364d8f6b155df3f2159dfca39f252abc81c76
Reviewed-on: https://review.whamcloud.com/39300
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>