Firmware filename fix, add another 8723BE ID

Thanks for looking after this code! Here's some patches to make it work with my hardware.

After going through this pain I'm driven to upstream it. Have you made any efforts on that front since 
http://patchwork.ozlabs.org/patch/234928/ ?

It looks like that patch is based on the driver in your `master` branch, which doesn't support my device.  However the driver in `new` does support my device and it also looks like it should support the 0x0bda:0x8723 device in the submission above.

The driver in `new` is also much easier to upstream, as now all it does is upload a firmware, no other changes are made to btusb.c. It looks like they found some wisdom and just made a firmware update that works with standard btusb interfaces.

I'd be happy to have a go at upstreaming that firmware upload routine, but don't want to conflict with anything you're doing. What do you think?