net: ena: remove code that does nothing

Both key and func parameters are pointers on the stack.
Setting them to NULL does nothing.
The original intent was to leave the key and func unset in this case,
but for this to happen nothing needs to be done as the calling
function ethtool_get_rxfh() already clears key and func.

This commit removes the above described useless code.

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>