ahci: asm1064: correct count of reported ports

The ASM1064 SATA host controller always reports wrongly,
that it has 24 ports. But in reality, it only has four ports.

before:
ahci 0000:04:00.0: SSS flag set, parallel bus scan disabled
ahci 0000:04:00.0: AHCI 0001.0301 32 slots 24 ports 6 Gbps 0xffff0f impl SATA mode
ahci 0000:04:00.0: flags: 64bit ncq sntf stag pm led only pio sxs deso sadm sds apst

after:
ahci 0000:04:00.0: ASM1064 has only four ports
ahci 0000:04:00.0: forcing port_map 0xffff0f -> 0xf
ahci 0000:04:00.0: SSS flag set, parallel bus scan disabled
ahci 0000:04:00.0: AHCI 0001.0301 32 slots 24 ports 6 Gbps 0xf impl SATA mode
ahci 0000:04:00.0: flags: 64bit ncq sntf stag pm led only pio sxs deso sadm sds apst

Signed-off-by: "Andrey Jr. Melnikov" <temnota.am@gmail.com>
Signed-off-by: Niklas Cassel <cassel@kernel.org>