rtlwifi: rtl8188ee: initialize packet_beacon

static code analysis from cppcheck reports:

[drivers/net/wireless/rtlwifi/rtl8188ee/trx.c:322]:
  (error) Uninitialized variable: packet_beacon

packet_beacon is not initialized and hence packet_beacon
contains garbage from the stack, so set it to false.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: Stable <stable@vger.kernel.org> [3.10+]
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>