wifi: rtw89: debug: Fix error handling in rtw89_debug_priv_btc_manual_set()

If there is a failure during kstrtobool_from_user()
rtw89_debug_priv_btc_manual_set should return a negative error code
instead of returning the count directly.

Fix this bug by returning an error code instead of a count after
a failed call of the function "kstrtobool_from_user". Moreover
I omitted the label "out" with this source code correction.

Fixes: e3ec7017 ("rtw89: add Realtek 802.11ax driver")
Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/tencent_1C09B99BD7DA9CAD18B00C8F0F050F540607@qq.com