stmmac: Fix build warnings.

In file included from drivers/net/stmmac/stmmac_ethtool.c:30:
drivers/net/stmmac/stmmac.h:111: warning: 'struct platform_device' declared inside parameter list
drivers/net/stmmac/stmmac.h:111: warning: its scope is only this definition or declaration, which is probably not what you want
drivers/net/stmmac/stmmac_main.c: In function 'stmmac_dvr_probe':
drivers/net/stmmac/stmmac_main.c:1744: warning: cast from pointer to integer of different size
In file included from drivers/net/stmmac/stmmac_mdio.c:31:
drivers/net/stmmac/stmmac.h:111: warning: 'struct platform_device' declared inside parameter list
drivers/net/stmmac/stmmac.h:111: warning: its scope is only this definition or declaration, which is probably not what you want
drivers/net/stmmac/dwmac1000_core.c: In function 'dwmac1000_dump_regs':
drivers/net/stmmac/dwmac1000_core.c:56: warning: cast from pointer to integer of different size

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>