net: ena: Change return value of ena_calc_io_queue_size() to void

ena_calc_io_queue_size() always returns 0, therefore make it a
void function and update the calling function to stop checking
the return value.

Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>