rtw88: coex: fix missing unitialization of variable 'interval'

Currently the variable 'interval' is not initialized and is only set
to 1 when oex_stat->bt_418_hid_existi is true.  Fix this by inintializing
variable interval to 0 (which I'm assuming is the intended default).

Addresses-Coverity: ("Uninitalized scalar variable")
Fixes: 5b2e9a35 ("rtw88: coex: add feature to enhance HID coexistence performance")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201203175142.1071738-1-colin.king@canonical.com

drivers/net/wireless/realtek/rtw88/coex.c

@@ -2051,7 +2051,7 @@ static void rtw_coex_action_bt_a2dp_hid(struct rtw_dev *rtwdev)
 	struct rtw_coex_dm *coex_dm = &coex->dm;
 	struct rtw_efuse *efuse = &rtwdev->efuse;
 	struct rtw_chip_info *chip = rtwdev->chip;
-	u8 table_case, tdma_case, interval;
+	u8 table_case, tdma_case, interval = 0;
 	u32 slot_type = 0;
 	bool is_toggle_table = false;