MdePkg/UefiSpec.h: Change comments of EFI_RESET_SYSTEM

MdePkg/UefiSpec.h: Change comments of EFI_RESET_SYSTEM

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1460

Refer to Uefi spec 2.8, the ResetData is valid while ResetStatus
is EFI_SUCCESS regardless of the ResetType is EfiResetPlatformSpecific
or not.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Michael Turner <Michael.Turner@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>