power: supply: apm_power: only unset own apm_get_power_status

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: 3788ec932bfd ("[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>