net: wireless/rtlwifi: fix uninitialized variable issue

The use of variable packet_beacon might be uninitialized in the two files,
which is same as this patch:
https://patchwork.kernel.org/patch/2006711/



Signed-off-by: Cong Ding <dinggnu@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>