DSPInterpreter: fix off-by-one errors in cycle counting

[Tilka]

Previously, when calling RunCycles(1) we would actually run two instructions. (We currently assume that all instructions take one cycle.)

[Pokechu22]

Note that the recompiler was not affected, as it uses JA (jump above/unsigned greater than):

dolphin/Source/Core/Core/DSP/Jit/x64/DSPEmitter.cpp

Lines 456 to 460 in ffdc853

	// Decrement cyclesLeft
	MOV(64, R(RCX), ImmPtr(&m_cycles_left));
	SUB(16, MatR(RCX), R(EAX));
	J_CC(CC_A, dispatcherLoop);

I don't know if the rest of the recompiler properly handles cycle counts though.