AHCI device access outside the drive on x86_64

[Kalamatee]

• [x] Describe the bug
  Installing to AHCI fails because it tries to write outside of the drive.

• [x] To Reproduce
  Steps to reproduce the behavior: Use InstallAROS to install to an attached ahci.device unit

• [x] Expected behaviour
  AROS to Install

• [ ] Screenshots
  

• [x] Architecture
  

• pc (native)

• [x] CPU
  

• i386

• x86_64

• [ ] Version
  

• [ ] Additional context