power: supply: qcom_battmgr: return EAGAIN when firmware service is not up

The driver returns -ENODEV when the firmware battmrg service hasn't
started yet, while per-se -ENODEV is fine, we usually use -EAGAIN to
tell the user to retry again later. And the power supply core uses
-EGAIN when the device isn't initialized, let's use the same return.

This notably causes an infinite spam of:
thermal thermal_zoneXX: failed to read out thermal zone (-19)
because the thermal core doesn't understand -ENODEV, but only
considers -EAGAIN as a non-fatal error.

While it didn't appear until now, commit [1] fixes thermal core
and no more ignores thermal zones returning an error at first
temperature update.

[1] 5725f40 ("thermal: core: Call monitor_thermal_zone() if zone temperature is invalid")

Link: https://lore.kernel.org/all/2ed4c630-204a-4f80-a37f-f2ca838eb455@linaro.org/
Cc: stable@vger.kernel.org
Fixes: 29e8142 ("power: supply: Introduce Qualcomm PMIC GLINK power supply")
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Reviewed-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Link: https://lore.kernel.org/r/20240715-topic-sm8x50-upstream-fix-battmgr-temp-tz-warn-v1-1-16e842ccead7@linaro.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: superna9999

drivers/power/supply/qcom_battmgr.c

@@ -486,7 +486,7 @@ static int qcom_battmgr_bat_get_property(struct power_supply *psy,
 	int ret;
 
 	if (!battmgr->service_up)
-		return -ENODEV;
+		return -EAGAIN;
 
 	if (battmgr->variant == QCOM_BATTMGR_SC8280XP)
 		ret = qcom_battmgr_bat_sc8280xp_update(battmgr, psp);
@@ -683,7 +683,7 @@ static int qcom_battmgr_ac_get_property(struct power_supply *psy,
 	int ret;
 
 	if (!battmgr->service_up)
-		return -ENODEV;
+		return -EAGAIN;
 
 	ret = qcom_battmgr_bat_sc8280xp_update(battmgr, psp);
 	if (ret)
@@ -748,7 +748,7 @@ static int qcom_battmgr_usb_get_property(struct power_supply *psy,
 	int ret;
 
 	if (!battmgr->service_up)
-		return -ENODEV;
+		return -EAGAIN;
 
 	if (battmgr->variant == QCOM_BATTMGR_SC8280XP)
 		ret = qcom_battmgr_bat_sc8280xp_update(battmgr, psp);
@@ -867,7 +867,7 @@ static int qcom_battmgr_wls_get_property(struct power_supply *psy,
 	int ret;
 
 	if (!battmgr->service_up)
-		return -ENODEV;
+		return -EAGAIN;
 
 	if (battmgr->variant == QCOM_BATTMGR_SC8280XP)
 		ret = qcom_battmgr_bat_sc8280xp_update(battmgr, psp);