wifi: rtw88: Drop h2c.lock

The h2c.lock spinlock is used in rtw_fw_send_h2c_command() and
rtw_fw_send_h2c_packet().  Most callers call this with rtwdev->mutex
held, except from one callsite in the debugfs code. The debugfs code
alone doesn't justify the extra lock, so acquire rtwdev->mutex in
debugfs and drop the now unnecessary spinlock.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221202081224.2779981-5-s.hauer@pengutronix.de