rtw88: fix TX secondary channel offset of 40M if current bw is 20M or 40M

rtw88: fix TX secondary channel offset of 40M if current bw is 20M or 40M

BugLink: https://bugs.launchpad.net/bugs/1780590
TX secondary channel offset is valid only if current bandwidth is 80M,
otherwise leave this value as zero. The wrong value of txsc40 causes
MAC unpredictable behavior.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
(cherry picked from commit 73a2d0b83424f7150a1f607470dac67c95b8b2d4)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>