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.