RaspiVid: Use correct data type for the result of raspicli_unmap_xref()
RaspiVid: Use correct data type for the result of raspicli_unmap_xref()

The raspicli_unmap_xref() function returns const char* which makes the
compiler complain.

6by9/userland,maroviher/userland,luked99/userland-1,JamesH65/userland,gonzoua/userland,adamheinrich/userland,kraj/userland,raspberrypi/userland,JamesH65/userland,6by9/userland,JamesH65/userland,raspberrypi/userland,adamheinrich/userland,luked99/userland-1,kraj/userland,adamheinrich/userland,kraj/userland,gonzoua/userland,raspberrypi/userland,maroviher/userland,6by9/userland,maroviher/userland,gonzoua/userland,luked99/userland-1