kbd: fix SRC_URI

* '/pub' is part of KERNELORG_MIRROR in oe-core already
* old OE had in bitbake.conf:KERNELORG_MIRROR = "http://kernel.org"
  and mirrors.bbclass:${KERNELORG_MIRROR}     http://www.kernel.org/pub



Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>