Reduce comparisons of size_t and int

`Const::size()` returns int, so change iterators that use it to `auto` instead of `size_t`.
For cases where size is being explicitly cast to `int`, use the wrapper that we already have instead: `Yosys::GetSize()`.

techlibs/quicklogic/ql_dsp_simd.cc

@@ -60,7 +60,7 @@ struct QlDspSimdPass : public Pass {
 
 	// ..........................................
 
-	const size_t m_ModeBitsSize = 80;
+	const int m_ModeBitsSize = 80;
 
 	// DSP parameters
 	const std::vector<std::string> m_DspParams = {"COEFF_3", "COEFF_2", "COEFF_1", "COEFF_0"};