cxgb4: Fix incorrect sequence numbers shown in devlog

Part of commit 49aa284fe64c4c1 ("cxgb4: Add support for devlog")
change introduced a real bug where the Device Log Sequence Numbers are
no longer being converted from firmware Big-Endian to local CPU-Endian
format.

This patch moves all of the translation into the devlog_show() routine.
The only endianness code now in devlog_open() is the small loop to find the
earliest (lowest Sequence Number) Device Log entry in the circular buffer.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>