Bluetooth: btusb: RTL8761BUV consistent naming

Based on photos available from the FCC, all currently supported RTL8761B
series USB dongles have the same chip: RTL8761BUV.

rtl8761bu is often used to refer to this chip.
rtl8761b sometimes refers to this chip, and other times to its
UART variant (RTL8761BTV).

+----------------+---------+---------+---------------+
|     Dongle     | USB VID | USB PID |    FCC ID     |
+----------------+---------+---------+---------------+
| ASUS USB-BT500 | 0x0b05  | 0x190e  | MSQ-USBBTJB00 |
| TP-Link UB500  | 0x2357  | 0x0604  | 2AXJ4UB500    |
| EDUP EP-B3519  |         |         | 2AHRD-EPB3519 |
| EDUP EP-B3536  |         |         | 2AHRDEP-B3536 |
| UGREEN CM390   |         |         | 2AQI5-CM390   |
+----------------+---------+---------+---------------+

Signed-off-by: Szabolcs Sipos <labuwx@balfug.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>