net: fsl: avoid 64-bit warning on pq_mdio

The pq_mdio driver can now be built for ARM64, where we get a format
string warning:

drivers/net/ethernet/freescale/fsl_pq_mdio.c: In function 'fsl_pq_mdio_probe':
drivers/net/ethernet/freescale/fsl_pq_mdio.c:467:25: warning: format '%x' expects argument of type 'unsigned int', but argument 3 has type 'long int' [-Wformat=]

The argument is an implicit ptrdiff_t from the subtraction of two pointers,
so we should use the %z format string modifier to make this work on 64-bit
architectures.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: fe761bcb ("net: fsl: expands dependencies of NET_VENDOR_FREESCALE")
Signed-off-by: David S. Miller <davem@davemloft.net>