kbuild, deb-pkg: Fix build with paranoid umask

umask 077
make deb-pkg
<snipp ..>
dpkg-deb: building package `linux-image-2.6.36+' in `../linux-image-2.6.36+_2.6.36+-4_amd64.deb'.
dpkg-deb: control directory has bad permissions 700 (must be >=0755 and <=0775)
make[1]: *** [deb-pkg] Error 2

Reported-by: Bastian Blank <waldi@debian.org>
Signed-off-by: maximilian attems <max@stro.at>
Signed-off-by: Michal Marek <mmarek@suse.cz>