PluggableUSB iSerialNum buffer overflow

[Legion2]

PluggableUSB_::getShortName and PluggableUSBModule::getShortName should not only get a char pointer as argument, but also the size of the buffer. I have currently the problem that i don't know how many chars I can copy to the pointer, without producing a overflow. So if other PluggableUSBModule's appended some characters, I have less space for my string. But currently I can't know that, because the remaining size of the buffer is not given.