staging: comedi: fix infoleak to userspace

commit 819cbb12 upstream.

driver_name and board_name are pointers to strings, not buffers of size
COMEDI_NAMELEN.  Copying COMEDI_NAMELEN bytes of a string containing
less than COMEDI_NAMELEN-1 bytes would leak some unrelated bytes.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>