kernel.bbclass: pass KERNEL_VERSION through legitimize_package_name

kernel.bbclass: pass KERNEL_VERSION through legitimize_package_name

- KERNEL_VERSION may contain characters unsuitable for package
  names, e.g. underscores. Use legitimize_package_name to replace
  those characters.

(From meta-openembedded rev: 2a4ffb47b04926ca43ccbab33364101f6459433a)

Signed-off-by: Andreas Oberritter <obi@opendreambox.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>