net: dsa: qca8k: fix an endian bug in qca8k_get_ethtool_stats()

The "hi" variable is a u64 but the qca8k_read() writes to the top 32
bits of it.  That will work on little endian systems but it's a bit
subtle.  It's cleaner to make declare "hi" as a u32.  We will still need
to cast it when we shift it later on in the function but that's fine.

Fixes: 7c9896e3 ("net: dsa: qca8k: check return value of read functions correctly")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>