kbuild: In setlocalversion change -git_dirty to just -dirty

When building Debian packages directly from the git tree, the appended
"git_dirty" is a problem due to the underscore.  In order to cause the
least problems, change that just to "dirty".

Signed-off-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/setlocalversion b/scripts/setlocalversion
index f54dac8..9a23825 100644
--- a/scripts/setlocalversion
+++ b/scripts/setlocalversion
@@ -17,6 +17,6 @@
 
 	# Are there uncommitted changes?
 	if git diff-files | read dummy; then
-		printf '%s' -git_dirty
+		printf '%s' -dirty
 	fi
 fi