MdeModulePkg AtaBusDxe: Fix ATA commands cannot be sent to some devices

If there is no port multiplier (PortMultiplierPort = 0xFFFF), current code
in functions TransferAtaDevice() and TrustTransferAtaDevice() will always
set the DEV bit of the ATA device register. It causes that ATA commands
cannot be sent to some ATA hard drives.

Cc: Feng Tian <feng.tian@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>