kernel: Bail-out if kernel config isn't set

* And remove stale info comment

Change-Id: I0cdd5ff54ed316858045f4c4ada4d78e593667cd
diff --git a/build/tasks/kernel.mk b/build/tasks/kernel.mk
index 386bca1..57612e6 100644
--- a/build/tasks/kernel.mk
+++ b/build/tasks/kernel.mk
@@ -142,9 +142,8 @@
         $(warning * Please add the TARGET_KERNEL_CONFIG variable to your   *)
         $(warning * BoardConfig.mk file                                    *)
         $(warning **********************************************************)
-        # $(error "NO KERNEL CONFIG")
+        $(error "NO KERNEL CONFIG")
     else
-        #$(info Kernel source found, building it)
         FULL_KERNEL_BUILD := true
         KERNEL_BIN := $(TARGET_PREBUILT_INT_KERNEL)
     endif