MdeModulePkg NvmExpressDxe: Refine GetNextNamespace API to follow spec

MdeModulePkg NvmExpressDxe: Refine GetNextNamespace API to follow spec

According to the UEFI spec,
EFI_NVM_EXPRESS_PASS_THRU_PROTOCOL.GetNextNamespace() should return
EFI_NOT_FOUND when the value pointed to by NamespaceId is the namespace ID
of the last namespace on the NVM Express controller. This commit modifies
the check for NamespaceId to follow this rule.

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>