wifi: rtw89: refine clearing supported bands to check 2/5 GHz first

We refine to check if supported bands of NL80211_BAND_2GHZ and
NL80211_BAND_5GHZ exist before freeing their iftype_data. For
now, it does not really encounter problems because all current
chips support both 2 GHz and 5 GHz. But, driver actually allows
chips to declare whether 2/5 GHz are supported or not. In case
some future chips really don't support them, we refine this code.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230602150556.36777-2-pkshih@realtek.com