builddeb: remove debian/files before build

Commit 3716001bcb ("deb-pkg: add source package") added the ability to
create a debian changelog file.  This exposed that previously the
builddeb script hasn't cleared debian/files between builds.

As debian/files keeps accumulating entries, the changes file will end up
growing indefinelty.  With outdated entries in debian/files, builddeb
script will exit with failure.  This regression impacts those who use
"make deb-pkg" target to build kernel into a .deb package and never use
"make mrproper" or other means to clean kernel tree from generated
directories.

To fix the regression, remove debian/files before starting build and in
the generated clean rule.

Fixes: 3716001bcb ("deb-pkg: add source package")
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reported-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Kalle Valo <kvalo@codeaurora.org>
Acked-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Michal Marek <mmarek@suse.cz>
Cc: maximilian attems <maks@stro.at>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/package/builddeb

@@ -115,7 +115,7 @@ esac
 BUILD_DEBUG="$(grep -s '^CONFIG_DEBUG_INFO=y' $KCONFIG_CONFIG || true)"
 
 # Setup the directory structure
-rm -rf "$tmpdir" "$fwdir" "$kernel_headers_dir" "$libc_headers_dir" "$dbg_dir"
+rm -rf "$tmpdir" "$fwdir" "$kernel_headers_dir" "$libc_headers_dir" "$dbg_dir" $objtree/debian/files
 mkdir -m 755 -p "$tmpdir/DEBIAN"
 mkdir -p "$tmpdir/lib" "$tmpdir/boot"
 mkdir -p "$fwdir/lib/firmware/$version/"
@@ -408,7 +408,7 @@ binary-arch:
 	\$(MAKE) KDEB_SOURCENAME=${sourcename} KDEB_PKGVERSION=${packageversion} bindeb-pkg
 
 clean:
-	rm -rf debian/*tmp
+	rm -rf debian/*tmp debian/files
 	mv debian/ debian.backup # debian/ might be cleaned away
 	\$(MAKE) clean
 	mv debian.backup debian