Windows: ensure buffer passed to HidD_SetFeature is large enough

[Mornix]

HidD_SetFeature() requires a feature report be at least a certain size similar to the requirement for WriteFile() in the implementation of hid_write().

[Youw]

Thanks, this is good.
Do you mind making a small change?
Cache the buffer as a device member, and allocate it only on first use.
An optimisation, so we don't do dynamica allocations on each report.

I wanted to apply same optimisation for hid_write to, just didn't have a chance to do so yet.

[Youw]

Nice!
This is exactly how I'd do it.