ath79: update image command for Plasma Cloud PA300

Commit 5fc28ef47959 ("ath79: Add support for Plasma Cloud PA300")
added the IMAGE/sysupgrade.bin/squashfs definition, which leaks into
other devices, resulting in sysupgrade.bin images that are actually
tarballs and do not boot when directly written to flash.

We can use the normal sysupgrade.bin command variable for this device.

Signed-off-by: Sven Wegener <[email protected]>
[fix format, spelling]
Signed-off-by: David Bauer <[email protected]>

target/linux/ath79/image/generic.mk

@@ -1623,7 +1623,7 @@ define Device/plasmacloud_pa300-common
   IMAGES += factory.bin
   KERNEL := kernel-bin | append-dtb | lzma | uImage lzma | pad-to $$(BLOCKSIZE)
   IMAGE/factory.bin := append-rootfs | pad-rootfs | openmesh-image ce_type=PA300
-  IMAGE/sysupgrade.bin/squashfs := append-rootfs | pad-rootfs | sysupgrade-tar rootfs=$$$$@ | append-metadata
+  IMAGE/sysupgrade.bin := append-rootfs | pad-rootfs | sysupgrade-tar rootfs=$$$$@ | append-metadata
 endef
 
 define Device/plasmacloud_pa300