MdeModulePkg/PciBus: Fix bug that PCI BUS claims too much resource

MdeModulePkg/PciBus: Fix bug that PCI BUS claims too much resource

The bug was caused by 728d74973c9262b6c7b7ef4be213223d55affec3
"MdeModulePkg/PciBus: Count multiple hotplug resource paddings".

The patch firstly updated the Bridge->Alignment to the maximum
alignment of all devices under the bridge, then aligned the
Bridge->Length to Bridge->Alignment.
It caused too much resources were claimed.

The new patch firstly aligns Bridge->Length to Bridge->Alignment,
then updates the Bridge->Alignment to the maximum alignment of all
devices under the bridge.
Because the step to update the Bridge->Alignment is to make sure
the resource allocated to the bus under the Bridge meets all
devices alignment. But the Bridge->Length doesn't have to align
to the maximum alignment.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>