Unfortunately, if you read man page from mspdebug, you will notice the following:
Connect to an eZ430-F2013 or a FET430UIF device. The device argument should be the filename of the appropriate tty device. The TI serial converter chips on these devices are supported by newer versions of the Linux kernel, and should appear as /dev/ttyXX when attached.
USB connection is not supported for this driver.
So it seems that you have to use serial connection instead of USB one.