wifi: rtl8xxxu: Use u32_get_bits in *_identify_chip

It simplifies the code a bit.

Suggested-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/68f94284-3728-7b75-2b7b-64fae8af6bc5@gmail.com