ata: ahci: use hweight_long() to count port_map bits

ata: ahci: use hweight_long() to count port_map bits

Replace the open loop used to calculate the number of set bits
in the port mapping with the `hweight_long()` function, which
simplifies the code without altering its functionality.

Signed-off-by: TanZheng <tanzheng@kylinos.cn>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>