UefiCpuPkg/MtrrLib: Fix MtrrDebugPrintAllMtrrsWorker to avoid hang

UefiCpuPkg/MtrrLib: Fix MtrrDebugPrintAllMtrrsWorker to avoid hang

ARRAY_SIZE(Mtrrs->Variables.Mtrr) was used in
MtrrDebugPrintAllMtrrsWorker() to parse the MTRR registers.
Instead, the actual variable MTRR count should be used.
Otherwise, the uninitialized random data in MtrrSetting may cause
MtrrLibSetMemoryType() hang.

Steven Shi found this bug in QEMU when using Q35 chip.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Steven Shi <steven.shi@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>