rockchip: switch to kernel 6.1

Required by the following rk3568 support.

Signed-off-by: Tianling Shen <[email protected]>

target/linux/rockchip/Makefile

@@ -7,8 +7,7 @@ BOARDNAME:=Rockchip
 FEATURES:=ext4 audio usb usbgadget display gpio fpu pci pcie rootfs-part boot-part squashfs
 SUBTARGETS:=armv8
 
-KERNEL_PATCHVER:=5.15
-KERNEL_TESTING_PATCHVER:=6.1
+KERNEL_PATCHVER:=6.1
 
 define Target/Description
 	Build firmware image for Rockchip SoC devices.