board/esd/cpci750/mv_eth.c: Fix GCC 4.6 build warnings

board/esd/cpci750/mv_eth.c: Fix GCC 4.6 build warnings

Fix:
mv_eth.c: In function 'mv64360_eth_real_open':
mv_eth.c:425:6: warning: variable 'port_status' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_stop':
mv_eth.c:643:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_xmit':
mv_eth.c:719:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_receive':
mv_eth.c:804:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_get_stats':
mv_eth.c:903:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_update_stat':
mv_eth.c:931:24: warning: variable 'dummy' set but not used [-Wunused-but-set-variable]
mv_eth.c:930:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'mv64360_eth_print_stat':
mv_eth.c:1012:15: warning: variable 'port_num' set but not used [-Wunused-but-set-variable]
mv_eth.c: In function 'eth_clear_mib_counters':
mv_eth.c:2069:15: warning: variable 'dummy' set but not used [-Wunused-but-set-variable

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Reinhard Arlt <reinhard.arlt@esd.eu>