debian: fix indentation in dh_makeshlibs

debian/rules is a Makefile, so recipes must be indented with tabs.

BUG=none
TEST=kokoro mesa job succeeds

Change-Id: If9e0f77854bf9cf1c881c7b201cad57261e33047
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/mesa/+/1718355
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
Commit-Queue: Stephen Barber <smbarber@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
diff --git a/debian/rules b/debian/rules
index 1bc3c5e..b63bca0 100755
--- a/debian/rules
+++ b/debian/rules
@@ -228,7 +228,7 @@
 	done
 
 override_dh_makeshlibs:
-  dh_makeshlibs -a -- -c3
+	dh_makeshlibs -a -- -c3
 
 %:
 	dh $@ --with quilt$(with_libva) \