IB/ehca: Export module parameters in sysfs

At the moment the ehca module parameters are not exported in sysfs.
Export them with 0444 permissions.

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>