linux-xlnx.inc: Fix reference to kernel branch
linux-xlnx.inc: Fix reference to kernel branch

The reference was not used in any xilinx code, however external recipes
may have relied on this value and loaded the wrong kernel.

Signed-off-by: Mark Hatle <41765ab18fb75e64ff0efe27f2ebcdb2d6f7e44e@xilinx.com>

Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx