MdeModulePkg/NvmExpress: Fix bug of handling not null-terminated strings

MdeModulePkg/NvmExpress: Fix bug of handling not null-terminated strings

In EnumerateNvmeDevNamespace(), when Private->ControllerData->Sn and/or
Private->ControllerData->Mn are NOT null-terminated strings,
UnicodeSPrintAsciiFormat(…) may generate unexpected (garbage) output
string.

Cc: Simon (Xiang) Lian-SSI <simon.lian@ssi.samsung.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Simon (Xiang) Lian-SSI <simon.lian@ssi.samsung.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>