mlxsw: fix warnings for big-endian 32-bit dma_addr_t

The recently added mlxsw driver produces warnings in ARM
allmodconfig:

drivers/net/ethernet/mellanox/mlxsw/pci.c: In function 'mlxsw_pci_cmd_exec':
drivers/net/ethernet/mellanox/mlxsw/pci.c:1585:59: warning: right shift count >= width of type [-Wshift-count-overflow]
linux/byteorder/big_endian.h:38:51: note: in definition of macro '__cpu_to_be32'
drivers/net/ethernet/mellanox/mlxsw/pci.c:76:2: note: in expansion of macro 'iowrite32be'

This uses upper_32_bits() to extract the bits while avoiding that warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Fixes: eda6500a "mlxsw: Add PCI bus implementation"
Signed-off-by: David S. Miller <davem@davemloft.net>