staging: lustre: debug: initialize debug_msg_data if needed

initialize the libcfs_debug_msg_data only if needed

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-1408
Reviewed-on: http://review.whamcloud.com/8338


Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>