AHCIController: Fix off-by-one mistake (SerenityOS#7144)

Fixes off-by-one caused by reading the register directly
without adding a 1 to it, because AHCI reports 1 less port than
the actual number of ports supported.

Kernel/Storage/AHCIController.cpp

@@ -183,7 +183,7 @@ RefPtr<StorageDevice> AHCIController::device_by_port(u32 port_index) const
 RefPtr<StorageDevice> AHCIController::device(u32 index) const
 {
  NonnullRefPtrVector<StorageDevice> connected_devices;
- for (size_t index = 0; index < (size_t)(hba().control_regs.cap & 0x1F); index++) {
+ for (size_t index = 0; index < capabilities().ports_count; index++) {
  auto checked_device = device_by_port(index);
  if (checked_device.is_null())
  continue;