wifi: rtw89: wow: cast nd_config->delay to u64 in tsf arithmetic

wifi: rtw89: wow: cast nd_config->delay to u64 in tsf arithmetic

The type of tsf arithmetic is
   u64 += u16 * int;

When (u16 * int) is larger than 0x7FFFFFFF, the value casting to u64 with
sign-extension will become all 1 in upper 32 bits part.

To meet the case, u16 value should be larger than 20491
(0x7FFFFFFF / 104800). Fortunately the meaning of 20491 is delay time of
WoWLAN net detection in unit of second, so 20491 seconds (5.7 hours)
might not a real case we can meet.

Addresses-Coverity-ID: 1620910 ("Unintended sign extension")

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20241009004300.8144-2-pkshih@realtek.com