WmiSetMark causes ReactOS to enter the debugger

When testing the XP explorer in ReactOS, upon starting up it will hit line 438 in wmidrv.c in ntoskrnl which is an UNIMPLEMENTED_DEBUGBREAK. To a new user to ReactOS trying the XP explorer in ReactOS, this might confuse them. The attached patch changes it to UNIMPLEMENTED instead of UNIMPLEMENTED_DEBUGBREAK. I tested this with the XP explorer and ReactOS did not enter the debugger.