wifi: rtlwifi: use unsigned long for rtl_bssid_entry timestamp

Since 'age' of 'struct rtl_bssid_entry' is in jiffies, prefer 'unsigned
long' over 'u32' to avoid possible truncation in 'rtl_collect_scan_list()'
and thus weird result in 'rtl_scan_list_expire()'. Compile tested only.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230929154524.222498-1-dmantipov@yandex.ru