[SCSI] qla2xxx: Don't depend on mailbox return values while enabling FCE tracing.

Recent firmwares no longer return the 'number of buffers' in
mailbox6.  The original code may result in a potential panic
during a FW-dump process due to the driver misinterpreting the
size of the allocated buffer.
Signed-off-by: NAndrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/qla2xxx/qla_mbx.c

@@ -2508,7 +2508,7 @@ qla2x00_enable_fce_trace(scsi_qla_host_t *ha, dma_addr_t fce_dma,
 		if (mb)
 			memcpy(mb, mcp->mb, 8 * sizeof(*mb));
 		if (dwords)
-			*dwords = mcp->mb[6];
+			*dwords = buffers;
 	}
 
 	return rval;