ipq40xx: switch to zImage kernel for SKSpruce WIA3300-20

The bootloader can support zImage linux kernel which can decrease
the firmware image size.

Signed-off-by: Shiji Yang <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16662
Signed-off-by: Robert Marko <[email protected]>

target/linux/ipq40xx/image/generic.mk

@@ -1093,7 +1093,7 @@ endef
 TARGET_DEVICES += qxwlan_e2600ac-c2
 
 define Device/skspruce_wia3300-20
-	$(call Device/FitImage)
+	$(call Device/FitzImage)
 	BLOCKSIZE := 64k
 	IMAGE_SIZE := 55104k
 	SOC := qcom-ipq4019