kirkwood: switch to Kernel 5.15 by default

Getting ready for the next release.

Signed-off-by: Paul Spooren <[email protected]>

target/linux/kirkwood/Makefile

@@ -11,8 +11,7 @@ FEATURES:=usb nand squashfs ramdisk
 CPU_TYPE:=xscale
 SUBTARGETS:=generic
 
-KERNEL_PATCHVER:=5.10
-KERNEL_TESTING_PATCHVER:=5.15
+KERNEL_PATCHVER:=5.15
 
 include $(INCLUDE_DIR)/target.mk