cxgb4: Avoid dumping Write-only registers in register dump

Avoid dumping MPS_RPLC_MAP_CTL for reg dumps; this is a Write-Only register.
Reading this register may cause MPS TCAM corruption.

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