net: ethernet: adi: adin1110: Fix uninitialized variable

The spi_transfer struct has to have all it's fields initialized to 0 in
this case, since not all of them are set before starting the transfer.
Otherwise, spi_sync_transfer() will sometimes return an error.

Fixes: a526a3cc

 ("net: ethernet: adi: adin1110: Fix SPI transfers")
Signed-off-by: Dell Jin <dell.jin.code@outlook.com>
Signed-off-by: Ciprian Regus <ciprian.regus@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>