rtlwifi: rtl8192de: remove the useless value assignment

The variable u4tmp is overwritten by the following call and the assignment
is useless, so remove it.

Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1605332735-9648-1-git-send-email-kaixuxia@tencent.com