staging: lustre: change ibh_mrs from array to pointer

With the removal of PMR we no longer require ibh_mrs field
to be a array so change it to a simple pointer.

Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6850
Reviewed-on: http://review.whamcloud.com/15788


Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Frank Zago <fzago@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>