kbuild: deb-pkg: avoid implicit effects

* The man page for dpkg-source(1) notes:

>      -b, --build directory [format-specific-parameters]
>             Build  a  source  package  (--build since dpkg 1.17.14).
>             <...>
>
>             dpkg-source will build the source package with the first
>             format found in this ordered list: the format  indicated
>             with  the  --format  command  line  option,  the  format
>             indicated in debian/source/format, “1.0”.  The  fallback
>             to “1.0” is deprecated and will be removed at some point
>             in the future, you should always  document  the  desired
>             source   format  in  debian/source/format.  See  section
>             SOURCE PACKAGE FORMATS for an extensive  description  of
>             the various source package formats.

  Thus it would be more foolproof to explicitly use 1.0 (as we always
  did) than to rely on dpkg-source's defaults.

* In a similar vein, debian/rules is not made executable by mkdebian,
  and dpkg-source warns about that but still silently fixes the file.
  Let's be explicit once again.

Signed-off-by: Arseny Maslennikov <ar@cs.msu.ru>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>