LU-3807 dcache: Unsafe error handling arnd ll_splice_alias

LU-3807 dcache: Unsafe error handling arnd ll_splice_alias

Callers of ll_splice_alias() should not assign the returned pointer to
the dentry since it can be an err pointer. Fixed the above bug using a
temporary dentry pointer. This temporary pointer is assigned to dentry
only if ll_splice_alias has not returned an err pointer.

Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Change-Id: I0cfdeb53b09fa5642ff01a919ded41aed32aad6d
Reviewed-on: http://review.whamcloud.com/7460
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>