Use types have same widths in loop condition.

In case comparisons between types of different widths in a loop condition
caused the loop to behave unexpectedly.

spirv_msl.cpp

@@ -4951,7 +4951,7 @@ void CompilerMSL::emit_custom_functions()
 
 			for (uint32_t variant = 0; variant < 12; variant++)
 			{
-				uint32_t dimensions = spv_func - SPVFuncImplArrayCopyMultidimBase;
+				uint8_t dimensions = spv_func - SPVFuncImplArrayCopyMultidimBase;
 				string tmp = "template<typename T";
 				for (uint8_t i = 0; i < dimensions; i++)
 				{

spirv_msl.hpp

@@ -638,7 +638,7 @@ public:
 protected:
 	// An enum of SPIR-V functions that are implemented in additional
 	// source code that is added to the shader if necessary.
-	enum SPVFuncImpl
+	enum SPVFuncImpl : uint8_t
 	{
 		SPVFuncImplNone,
 		SPVFuncImplMod,