wifi: rtlwifi: use unsigned long for bt_coexist_8723 timestamp

Since 'bt_inq_page_start_time' of 'struct bt_coexist_8723' is
in jiffies, prefer 'unsigned long' over 'u32' to avoid possible
truncation in 'rtl8723e_dm_bt_inq_page_monitor()' and adjust
related code. Found with clang's -Wshorten-64-to-32, 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/20231004092418.73337-1-dmantipov@yandex.ru