UefiCpuPkg/MtrrLib: Correct debug message

UefiCpuPkg/MtrrLib: Correct debug message

When printing the ascii format of memory attribute in debug message,
%s was used, but %a should be used.
The patch additionally changes %x to %r for EFI_STATUS.

The whole patch doesn't impact functionality of the MtrrLib.
Just debug message fix.

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