MdeModulePkg NvmExpressDxe: Refine GetNameSpace API to follow spec
    
    According to the UEFI spec,
    EFI_NVM_EXPRESS_PASS_THRU_PROTOCOL.GetNamespace() should return
    EFI_NOT_FOUND when the input DevicePath is a device path node type that
    the NVM Express Pass Thru driver supports, but there is not a valid
    translation from DevicePath to a namespace ID. Current code will return
    EFI_SUCCESS. This commit adds additional check in the GetNameSpace API to
    make sure correct status is returned.
    
    Cc: Feng Tian <feng.tian@intel.com>
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Hao Wu <hao.a.wu@intel.com>
    Reviewed-by: Feng Tian <feng.tian@intel.com>