ARM: ixp4xx: use normal prototype for {read,write}s{b,w,l}

ixp4xx defines the arguments to its __indirect_writesb() and other
functions as pointers to fixed-size data. This is not necessarily
wrong, and it works most of the time, but it causes warnings in
at least one driver:

drivers/net/ethernet/smsc/smc91x.c: In function 'smc_rcv':
drivers/net/ethernet/smsc/smc91x.c:495:21: error: passing argument 2 of '__indirect_readsw' from incompatible pointer type [-Werror=incompatible-pointer-types]
   SMC_PULL_DATA(lp, data, packet_len - 4);

All other definitions of the same functions pass void pointers,
so doing the same here avoids the warnings.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Krzysztof Halasa <khalasa@piap.pl>