sifiveu: switch to kernel v6.1

Enable kernel v6.1 as the default kernel for sifiveu.

Signed-off-by: Zoltan HERPAI <[email protected]>

target/linux/sifiveu/Makefile

@@ -11,8 +11,7 @@ FEATURES:=ext4
 KERNELNAME:=Image dtbs
 SUBTARGETS:=generic
 
-KERNEL_PATCHVER:=5.15
-KERNEL_TESTING_PATCHVER:=6.1
+KERNEL_PATCHVER:=6.1
 
 include $(INCLUDE_DIR)/target.mk