Simplify single device list handling

Simplify single device list handling

Some driver scan() functions only ever return a single device. For those it
is possible to slightly simplify the handling of the device list by
creating it on demand when the function returns.

Some drivers also have the following expression:
	devices = g_slist_append(devices, sdi);
	...
	if (!devices)
		...

This check will never evaluate to false so it is dropped as well.

Signed-off-by: Lars-Peter Clausen <redacted>