net: ethernet: chelsio: cxgb3: mc5.c: Remove some unused functions

Removes some functions that are not used anywhere:
dbgi_rd_rsp3() dbgi_wr_addr3()

This was partially found by using a static code analysis program called cppcheck.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: David S. Miller <davem@davemloft.net>