wifi: rtw88: Remove duplicate NULL check before calling usb_kill/free_urb()

wifi: rtw88: Remove duplicate NULL check before calling usb_kill/free_urb()

Both usb_kill_urb() and usb_free_urb() do the NULL check itself, so there
is no need to duplicate it prior to calling.

Fixes: a82dfd33d123 ("wifi: rtw88: Add common USB chip support")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231008025852.1239450-1-ruanjinjie@huawei.com