power: supply: bq27xxx: restrict no-battery detection to bq27000

There are fuel gauges in the bq27xxx series (e.g. bq27z561) which may in some
cases report 0xff as the value of BQ27XXX_REG_FLAGS that should not be
interpreted as "no battery" like for a disconnected battery with some built
in bq27000 chip.

So restrict the no-battery detection originally introduced by

    commit 3dd843e ("bq27000: report missing device better.")

to the bq27000.

There is no need to backport further because this was hidden before

	commit f16d9fb ("power: supply: bq27xxx: Retrieve again when busy")

Fixes: f16d9fb ("power: supply: bq27xxx: Retrieve again when busy")
Suggested-by: Jerry Lv <Jerry.Lv@axis.com>
Cc: stable@vger.kernel.org
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Link: https://lore.kernel.org/r/dd979fa6855fd051ee5117016c58daaa05966e24.1755945297.git.hns@goldelico.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: goldelico

drivers/power/supply/bq27xxx_battery.c

@@ -1919,8 +1919,8 @@ static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
 	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
 
 	cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
-	if ((cache.flags & 0xff) == 0xff)
-		cache.flags = -ENODEV; /* read error */
+	if (di->chip == BQ27000 && (cache.flags & 0xff) == 0xff)
+		cache.flags = -ENODEV; /* bq27000 hdq read error */
 	if (cache.flags >= 0) {
 		cache.capacity = bq27xxx_battery_read_soc(di);