MdeModulePkg/PciSioSerialDxe: Fix compiler warnings

MdeModulePkg/PciSioSerialDxe: Fix compiler warnings

Add missing braces in module global mControllerDevicePathTemplate.
Initialize ControllerNumber and ContainsControllerNode in
SerialControllerDriverStart() to address warning for potential use
before initialization warning.
Move initialization of local SerialIo earlier in
SerialControllerDriverStart() to address warning for potential use
before initialization warning.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19232 6f19259b-4bc3-4df7-8a09-765794883524