LU-4189 mdc: Removed unneeded NULL check

LU-4189 mdc: Removed unneeded NULL check

Do not bother checking the return value of changelog_kuc_hdr()
against NULL since this value was dereferenced earlier.

Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Change-Id: I34a81e840838e3b50bca0099fb810815b540875e
Reviewed-on: http://review.whamcloud.com/12919
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>