LU-1337 llite: take trunc_sem outside cl_io_loop for mkwrite

LU-1337 llite: take trunc_sem outside cl_io_loop for mkwrite

In truncate path it acquires lli_trunc_sem and then dlm lock, so
in page_mkwrite we should take it in the same sequence to avoid
dead lock.

This is a fix for f78805dbf041bb42b250fe754dff7b864856203f .

Signed-off-by: Liu Xuezhao <xuezhao.liu@emc.com>
Change-Id: Idb5574bffdaf00461befd43b867cdd9b3e549efe
Reviewed-on: http://review.whamcloud.com/4485
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>