UefiCpuPkg/CpuMpPei: Fix wrong CpuData pointer

CpuData buffer should be located in allocated buffer instead of at end of
WakeupBuffer.

(Sync patch r18550 from main trunk.)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <[email protected]>
Reviewed-by: Star Zeng <[email protected]>

git-svn-id: https://svn.code.sf.net/p/edk2/code/branches/UDK2015@18552 6f19259b-4bc3-4df7-8a09-765794883524