ibmvscsis: Fix max transfer length

Current code incorrectly calculates the max transfer length, since
it is assuming a 4k page table, but ppc64 all run on 64k page tables.

Cc: stable@vger.kernel.org
Reported-by: Steven Royer <seroyer@linux.vnet.ibm.com>
Tested-by: Steven Royer <seroyer@linux.vnet.ibm.com>
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>

drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c

@@ -46,6 +46,7 @@
 
 #define	INITIAL_SRP_LIMIT	800
 #define	DEFAULT_MAX_SECTORS	256
+#define MAX_TXU			1024 * 1024
 
 static uint max_vdma_size = MAX_H_COPY_RDMA;
 
@@ -1443,7 +1444,7 @@ static long ibmvscsis_adapter_info(struct scsi_info *vscsi,
 	info->mad_version = cpu_to_be32(MAD_VERSION_1);
 	info->os_type = cpu_to_be32(LINUX);
 	memset(&info->port_max_txu[0], 0, sizeof(info->port_max_txu));
-	info->port_max_txu[0] = cpu_to_be32(128 * PAGE_SIZE);
+	info->port_max_txu[0] = cpu_to_be32(MAX_TXU);
 
 	dma_wmb();
 	rc = h_copy_rdma(sizeof(*info), vscsi->dds.window[LOCAL].liobn,