Most platforms use void pointer arguments in these functions, but
ixp4xx does not, which triggers lots of warnings in device drivers like:

net/ethernet/8390/ne2k-pci.c: In function 'ne2k_pci_get_8390_hdr':
net/ethernet/8390/ne2k-pci.c:503:3: warning: passing argument 2 of 'insw' from incompatible pointer type
   insw(NE_BASE + NE_DATAPORT, hdr, sizeof(struct e8390_pkt_hdr)>>1);
   ^
In file included from include/asm/io.h:214:0,
                 from /git/arm-soc/include/linux/io.h:22,
                 from /git/arm-soc/include/linux/pci.h:31,
                 from net/ethernet/8390/ne2k-pci.c:48:
mach-ixp4xx/include/mach/io.h:316:91: note: expected 'u16 *' but argument is of type 'struct e8390_pkt_hdr *'
 static inline void insw(u32 io_addr, u16 *vaddr, u32 count)

Fixing the drivers seems hopeless, so this changes the ixp4xx code
to do the same as the others to avoid the warnings.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Krzysztof Halasa <khalasa@piap.pl>
Cc: Imre Kaloz <kaloz@openwrt.org>