wifi: rtw89: use passed channel in set_tx_shape_dfir()

In path of setting channel and setting TX power, the rtw89_chan instance
to be used is controlled by top and passed down. The set_tx_shape_dfir()
is in path of setting TX power, so it should use the passed rtw89_chan
instead of querying it itself. Otherwise, it might encounter mismatch
between parameters if multi-channel.

For example,
rtw89_8852ce 0000:04:00.0: set tx shape dfir by unknown ch: 155 on 2GHz

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/20230201032057.7349-1-pkshih@realtek.com