kbuild, deb-pkg: Check if KBUILD_IMAGE exists before copying it

Avoid an error when doing cp over the image when it does not contain
the full path to the file.

Signed-off-by: Guillem Jover <[e-mail]>
Signed-off-by: Michal Marek <[e-mail]>

scripts/package/builddeb

···
 	cp System.map "$tmpdir/boot/System.map-$version"
 	cp .config "$tmpdir/boot/config-$version"
 	# Not all arches include the boot path in KBUILD_IMAGE
-	if ! cp $KBUILD_IMAGE "$tmpdir/boot/vmlinuz-$version"; then
+	if [ -e $KBUILD_IMAGE ]; then
+		cp $KBUILD_IMAGE "$tmpdir/boot/vmlinuz-$version"
+	else
 		cp arch/$ARCH/boot/$KBUILD_IMAGE "$tmpdir/boot/vmlinuz-$version"
 	fi
 fi