If our device only has a discrete number of DPIs, pass it on as-is to
libratbag rather than pretending it's a range and then failing to set the
DPIs.
For the actual ranged devices we use libratbag's now-exponential range
mapping rather than passing all possible ones on. This relies on us having the
same steps that libratbag uses, should be safe enough.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>