wifi: rtw88: 8703b: Fix reported RX band width

The definition of GET_RX_DESC_BW is incorrect. Fix it according to the
GET_RX_STATUS_DESC_BW_8703B macro from the official driver.

Tested only with RTL8812AU, which uses the same bits.

Cc: stable@vger.kernel.org
Fixes: 9bb762b3 ("wifi: rtw88: Add definitions for 8703b chip")
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Tested-by: Fiona Klute <fiona.klute@gmx.de>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/1cfed9d5-4304-4b96-84c5-c347f59fedb9@gmail.com