MdeModulePkg NvmExpressDxe: Refine GetNameSpace API to follow spec

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>