rtw88: refine unwanted h2c command

Don't send beacon filter h2c when there is no valid context.
Return early instead of printing out warning messages, so others
won't get confused.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210528032901.12927-3-pkshih@realtek.com