Constant folding: Correct result type of non-square matrix folding.

This also made the function easier to read by identifying
left and right operands more clearly.
diff --git a/SPIRV/GlslangToSpv.cpp b/SPIRV/GlslangToSpv.cpp
index e1babc1..a2e8a9e 100755
--- a/SPIRV/GlslangToSpv.cpp
+++ b/SPIRV/GlslangToSpv.cpp
@@ -229,7 +229,7 @@
 spv::Decoration TranslatePrecisionDecoration(const glslang::TType& type)
 {
     switch (type.getQualifier().precision) {
-    case glslang::EpqLow:    return spv::DecorationRelaxedPrecision; // TODO: Map instead to 16-bit types?
+    case glslang::EpqLow:    return spv::DecorationRelaxedPrecision;
     case glslang::EpqMedium: return spv::DecorationRelaxedPrecision;
     case glslang::EpqHigh:   return spv::NoPrecision;
     default: