staging: lustre: osc: fix max_dirty_mb tunable setting limit

staging: lustre: osc: fix max_dirty_mb tunable setting limit

The OSC tunable max_dirty_mb must be set to a value strictly lower
than 2048, as it is assumed by OSS in ofd_grant_alloc() routine.

Signed-off-by: Gregoire Pichon <gregoire.pichon@bull.net>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7218
Reviewed-on: http://review.whamcloud.com/16652
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>