linux-mainline: Added LINUX_VERSION variable

Fixes:

File "/home/retpolanne/Dev/orange-pi-one-plus-image/poky/scripts/lib/devtool/standard.py", line 839, in modify
if (os.path.exists(srcdir) and os.listdir(srcdir)) and (kernelVersion in staging_kerVer and staging_kbranch == kbranch):
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'in ' requires string as left operand, not NoneType

While running devtool modify virtual/kernel.


Signed-off-by: Marek Belisko <marek.belisko@gmail.com>

recipes-kernel/linux/linux-mainline.inc

@@ -7,6 +7,8 @@ inherit kernel
 
 require linux.inc
 
+LINUX_VERSION = "${PV}"
+
 KERNEL_DTB_PREFIX = "0"
 
 python() {