LU-506 kernel: remove BKL fix

LU-506 kernel: remove BKL fix

Commit I8a3432ad56b7a1fcdbf74be4b7819edb31bf6272 has defect; it's
fixed in this patch:
* use #ifdef instead of #if for HAVE_KERNEL_LOCKED check.
* in case of HAVE_KERNEL_LOCKED, a mntput() is missed if kernel is
  not locked.

Signed-off-by: Lai Siyao <laisiyao@whamcloud.com>
Change-Id: I5c93252dc02e0ff90ce108701f9d847e4ee2e4e6
Reviewed-on: http://review.whamcloud.com/2928
Tested-by: Hudson
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>