mdadm: pass CHECK_RUN_DIR=0 to the Makefile in order to fix build failure

This commit should fix build failures of mdadm 3.3:

  http://autobuild.buildroot.net/results/b4a/b4abc317d07b073f8be870ff0e7fee8f8c65f2ff/
  http://autobuild.buildroot.net/results/79e/79e6c5081a5197c4f4647db497fbd1e27f29714d/
  http://autobuild.buildroot.net/results/224/2242f8284aa4bdbb0ab959a6a6464f20fa043e2f/



Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>