[Cuda] Simplify the 'getMaxRegistersJitOptionValue' utility and its use

[GeorgeWeb]

This change simplifies the getMaxRegistersJitOptionValue function as it was previously unclear what the return bool value actually meant, because it doesn't really signify whether the value was valid or not but it was more of a whether the parsing was successful. Now we just check if the parsed value is different from the default value for CU_JIT_MAX_REGISTERS and if it is, we add it to the list of options.