MdeModulePkg/AtaAtapiPassThru: unmap DMA buffers after disabling BM DMA

MdeModulePkg/AtaAtapiPassThru: unmap DMA buffers after disabling BM DMA

In AtaAtapiPassThruStop(), if the device has been operating in AHCI mode,
we unmap the DMA buffers and then disable the device (including bus master
DMA). The order of these actions is wrong; we shouldn't unmap DMA buffers
until bus master DMA is turned off. Reverse the steps.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>