Fix several code review minor comments:

Fix several code review minor comments:
1. Line 79:Use the pre-initialized global variable mPoolHeadList = INITIALIZE_LIST_HEAD_VARIABLE (mPoolHeadList) to remove the statement in line 102
2. Line 337: The debug print statement: “Addr = %x” should change to “Addr = %p” since the expected Buffer is VOID *; How about “(len %x) %,d” ? The Size & Pool->Used belong to type UINTN? Cast it to UINT64 and use %lx
3.Line 413, 418, 425, 477: Use “Buffer != NULL” instead of “NULL != Buffer”
4. Line 451: The debug print statement: “FreePool = %x” should change to FreePool = %p” since Head->Data is pointer; How about “(len %x) %,d” ? The Head->Size& Pool->Used belong to type UINTN? Cast it to UINT64 and use %lx

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5916 6f19259b-4bc3-4df7-8a09-765794883524