MdeModulePkg NvmExpressDxe: return error code in error path

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=937

In NvmeExpressPassthru.c near line 659:
    Prp = NvmeCreatePrpList (
            PciIo,
            PhyAddr,
            EFI_SIZE_TO_PAGES(Offset + Bytes) - 1,
            &PrpListHost,
            &PrpListNo,
            &MapPrpList
            );
    if (Prp == NULL) {
      goto EXIT;
    }
Status is not set to an error code - Status is initialized to
EFI_SUCCESS, or set by a PciIo->Map to EFI_SUCCESS above this
code. This error path should set Status to an error code before
goto EXIT.

Change-Id: I8a5cdf981aa609534c205d3676395805ac60a003
Cc: Hao Wu <hao.a.wu@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Michael Turner <Michael.Turner@microsoft.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>