power: supply: apm_power: only unset own apm_get_power_status

Mirroring drivers/macintosh/apm_emu.c, this means that
  modprobe apm_power && modprobe $anotherdriver && modprobe -r apm_power
leaves $anotherdriver's apm_get_power_status instead of deleting it.

Fixes: 3788ec9 ("[BATTERY] APM emulation driver for class batteries")
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Link: https://patch.msgid.link/xczpgox57hxbunkcbdl5fxhc4gnsajsipldfidi7355afezk64@tarta.nabijaczleweli.xyz
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: nabijaczleweli

drivers/power/supply/apm_power.c

@@ -364,7 +364,8 @@ static int __init apm_battery_init(void)
 
 static void __exit apm_battery_exit(void)
 {
-	apm_get_power_status = NULL;
+	if (apm_get_power_status == apm_battery_apm_get_power_status)
+		apm_get_power_status = NULL;
 }
 
 module_init(apm_battery_init);