MdeModulePkg XhciDxe: Fix Map and Unmap inconsistency

MdeModulePkg XhciDxe: Fix Map and Unmap inconsistency

We found there are loops of *2* Maps and only *1* Unmap and
the DMA buffer address is decreasing.

It is caused by the below code flow.
XhcAsyncInterruptTransfer ->
  XhcCreateUrb ->
    XhcCreateTransferTrb ->
      Map Urb->DataMap           (1)

Timer: loops of *2* Maps and only *1* Unmap
XhcMonitorAsyncRequests ->
  XhcFlushAsyncIntMap ->
    Unmap and Map Urb->DataMap   (2)
  XhcUpdateAsyncRequest ->
    XhcCreateTransferTrb ->
      Map Urb->DataMap           (3)

This patch is to eliminate (3).

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>