[source] build: Fix not altering KERNELRELEASE for external kernel

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/3ce60ba0a163636c968c4046894beca0efe1907e

commit 3ce60ba0a163636c968c4046894beca0efe1907e
Author: Hauke Mehrtens <hauke at hauke-m.de>
AuthorDate: Sun Jun 18 23:27:51 2017 +0200

    build: Fix not altering KERNELRELEASE for external kernel
    
    When an external kernel tree is used the version should not get
    modified by the LEDE build scripts. This was added by Florian some time
    ago.
    The commit 0aed054becb21439 ("build: add KERNEL_MAKE and
    KERNEL_MAKE_FLAGS variables and move to kernel.mk") breaks this feature
    introduced in b6746a6ffb73 ("include: Do not alter KERNELRELEASE for
    external/git kernels").
    
    Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
 include/kernel.mk | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/kernel.mk b/include/kernel.mk
index 464c945..7674f0d 100644
--- a/include/kernel.mk
+++ b/include/kernel.mk
@@ -108,11 +108,10 @@ KERNEL_MAKE_FLAGS := \
 	CONFIG_SHELL="$(BASH)" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
 	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID)) \
-	KERNELRELEASE=$(LINUX_VERSION) \
 	cmd_syscalls=
 
 ifeq ($(call qstrip,$(CONFIG_EXTERNAL_KERNEL_TREE))$(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI)),)
-  KERNEL_MAKEOPTS += \
+  KERNEL_MAKE_FLAGS += \
 	KERNELRELEASE=$(LINUX_VERSION)
 endif