firedtv: fix registration - adapter number could only be zero

There was a bug causing the initialization to fail if adapter number was
greater than zero. The adapter was however registered which caused the driver
to oops the second time initialization was tried.

Signed-off-by: Henrik Kurelid <henrik@kurelid.se>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>