[smc9000] Avoid unused variable warning in gcc 4.6

Reported-by: Ralph Giles <giles@thaumas.net>
Tested-by: Ralph Giles <giles@thaumas.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/smc9000.c

     word my_phy_caps; // My PHY capabilities
     word my_ad_caps; // My Advertised capabilities
     word status;
-    int failed = 0;
     int rpc_cur_mode = RPC_DEFAULT;
     int lastPhy18;
 
     if (timeout < 1)
     {
         PRINTK2("PHY auto-negotiate timed out\n");
-        failed = 1;
     }
 
     // Fail if we detected an auto-negotiate remote fault
     if (status & PHY_STAT_REM_FLT)
     {
         PRINTK2("PHY remote fault detected\n");
-        failed = 1;
     }
 
     // Set our sysctl parameters to match auto-negotiation results