cxgb4: Fixes static checker warning in mps_tcam_show()

The commit 115b56af ("cxgb4: Update mps_tcam output to include T6
fields") from Dec 23, 2015, leads to the following static checker
warning:

        drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c:1735
mps_tcam_show()
        warn: we tested 'lookup_type' before and it was 'true'

Fixing it.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>