cam: options: Fix string concatenation

Adding an integer value to a char pointer doesn't concatenate strings,
it indexes in the pointed string. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/options.cpp

@@ -530,7 +530,7 @@ void OptionsParser::parseValueError(const Option &option)
 	if (option.name)
 		optionName = "--" + std::string(option.name);
 	else
-		optionName = "-" + static_cast<char>(option.opt);
+		optionName = "-" + std::string(1, option.opt);
 
 	std::cerr << "Can't parse " << option.typeName()
 		  << " argument for option " << optionName << std::endl;