[mutter] Fix incorrect 'is' in gen_default_modes

[Jonas Ådahl <jadahl src gnome org>]

commit 5b1620475e5ae5062f5b5100114bd04e84223ea2
Author: Sergio Costas <raster rastersoft com>
Date:   Mon Feb 10 20:32:07 2020 +0100

    Fix incorrect 'is' in gen_default_modes
    
    During compilation, gen_default_modes.py shows two warnings that
    say that a comparison is using 'is' instead of '=='.
    
    This patch fixes this bug.
    
    Fixes https://gitlab.gnome.org/GNOME/mutter/issues/985

 src/backends/native/gen-default-modes.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/backends/native/gen-default-modes.py b/src/backends/native/gen-default-modes.py
index aeccc0d28..fed514d45 100755
--- a/src/backends/native/gen-default-modes.py
+++ b/src/backends/native/gen-default-modes.py
@@ -62,9 +62,9 @@ output_lines = [
 
 def sync_flags(hsync, vsync):
     flags = "DRM_MODE_FLAG_"
-    flags += "NHSYNC" if hsync[0] is '-' else "PHSYNC"
+    flags += "NHSYNC" if hsync[0] == '-' else "PHSYNC"
     flags += " | DRM_MODE_FLAG_"
-    flags += "NVSYNC" if vsync[0] is '-' else "PVSYNC"
+    flags += "NVSYNC" if vsync[0] == '-' else "PVSYNC"
     return flags
 
 def drm_mode_info_from_modeline(line):