staging: lustre: osc: fix bug when setting max_pages_per_rpc

After setting like "lctl set_param -P osc.*.max_pages_per_rpc", it
is possible that the function osc_obd_max_pages_per_rpc_seq_write
will be called before ocd_brw_size has been set when mount.
ocd_brw_size is meaningless when it is zero. So it should not be
the limit at that time.
Signed-off-by: Wu Libin <lwu@ddn.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6421
Reviewed-on: http://review.whamcloud.com/14333Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.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>

drivers/staging/lustre/lustre/osc/lproc_osc.c

@@ -585,7 +585,8 @@ static ssize_t max_pages_per_rpc_store(struct kobject *kobj,
 	chunk_mask = ~((1 << (cli->cl_chunkbits - PAGE_SHIFT)) - 1);
 	/* max_pages_per_rpc must be chunk aligned */
 	val = (val + ~chunk_mask) & chunk_mask;
-	if (val == 0 || val > ocd->ocd_brw_size >> PAGE_SHIFT) {
+	if (!val || (ocd->ocd_brw_size &&
+		     val > ocd->ocd_brw_size >> PAGE_SHIFT)) {
 		return -ERANGE;
 	}
 	spin_lock(&cli->cl_loi_list_lock);