ui: Use g_new() & friends where that makes obvious sense

g_new(T, n) is neater than g_malloc(sizeof(T) * n).  It's also safer,
for two reasons.  One, it catches multiplication overflowing size_t.
Two, it returns T * rather than void *, which lets the compiler catch
more type errors.

This commit only touches allocations with size arguments of the form
sizeof(T).  Same Coccinelle semantic patch as in commit b45c03f.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/ui/sdl.c b/ui/sdl.c
index 3be2910..570cb99 100644
--- a/ui/sdl.c
+++ b/ui/sdl.c
@@ -985,7 +985,7 @@
         sdl_grab_start();
     }
 
-    dcl = g_malloc0(sizeof(DisplayChangeListener));
+    dcl = g_new0(DisplayChangeListener, 1);
     dcl->ops = &dcl_ops;
     register_displaychangelistener(dcl);