net: ena: fix error returning in ena_com_get_hash_function()

[ Upstream commit e9a1de378dd46375f9abfd8de1e6f59ee114a793 ]

In case the "func" parameter is NULL we now return "-EINVAL".
This shouldn't happen in general, but when it does happen, this is the
proper way to handle it.

We also check func for NULL in the beginning of the function, as there
is no reason to do all the work and realize in the end of the function
it was useless.

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