rtlwifi: Fix leak of skb when processing C2H_BT_INFO

With commit 0a9f8f0a ("rtlwifi: fix btmpinfo timeout while processing
C2H_BT_INFO"), calling rtl_c2hcmd_enqueue() with rtl_c2h_fast_cmd() true,
the routine returns without freeing that skb, thereby leaking it.

This issue has been discussed at https://github.com/lwfinger/rtlwifi_new/issues/401
and the fix tested there.

Fixes: 0a9f8f0a

 ("rtlwifi: fix btmpinfo timeout while processing C2H_BT_INFO")
Reported-and-tested-by: Francisco Machado Magalhães Neto <franmagneto@gmail.com>
Cc: Francisco Machado Magalhães Neto <franmagneto@gmail.com>
Cc: Ping-Ke Shih <pkshih@realtek.com>
Cc: Stable <stable@vger.kernel.org> # 4.18+
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>