deb-pkg: Fix building outside of source tree (O=...).

When building linux-headers package using deb-pkg, builddeb erroneously assume
current directory is the source tree. This is not true if building in another
directory, using make O=... deb-pkg.

This patch fix this problem.
Signed-off-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Tested-by: Nikolai Kondrashov <spbnick@gmail.com>
Acked-by: maximilian attems <max@stro.at>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/package/builddeb

@@ -238,12 +238,12 @@ EOF
 fi
 
 # Build header package
-find . -name Makefile -o -name Kconfig\* -o -name \*.pl > /tmp/files$$
-find arch/$SRCARCH/include include scripts -type f >> /tmp/files$$
+(cd $srctree; find . -name Makefile -o -name Kconfig\* -o -name \*.pl > /tmp/files$$)
+(cd $srctree; find arch/$SRCARCH/include include scripts -type f >> /tmp/files$$)
 (cd $objtree; find .config Module.symvers include scripts -type f >> /tmp/objfiles$$)
 destdir=$kernel_headers_dir/usr/src/linux-headers-$version
 mkdir -p "$destdir"
-tar -c -f - -T /tmp/files$$ | (cd $destdir; tar -xf -)
+(cd $srctree; tar -c -f - -T /tmp/files$$) | (cd $destdir; tar -xf -)
 (cd $objtree; tar -c -f - -T /tmp/objfiles$$) | (cd $destdir; tar -xf -)
 rm -f /tmp/files$$ /tmp/objfiles$$
 arch=$(dpkg --print-architecture)