net: thunderx: Fix OOPs with ethtool --register-dump

The ethtool_ops .get_regs function attempts to read the nonexistent
register NIC_QSET_SQ_0_7_CNM_CHG, which produces a "bus error" type
OOPs.

Fix by not attempting to read, and removing the definition of,
NIC_QSET_SQ_0_7_CNM_CHG.  A zero is written into the register dump to
keep the layout unchanged.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: <stable@vger.kernel.org> # 4.4.x-
Signed-off-by: David S. Miller <davem@davemloft.net>