wifi: rtl8xxxu: Rename rtl8xxxu_8188f_channel_to_group

This name is an anomaly. Change it to rtl8188f_channel_to_group to
follow the same pattern as the other functions.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Acked-by: Jes Sorensen <jes@trained-monkey.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/ba8e3ea2-74f5-e1db-296e-4ae5f03084dc@gmail.com