drm/ast: Do not include <linux/export.h>

Fix the compile-time warning

  drivers/gpu/drm/ast/ast_mode.c: warning: EXPORT_SYMBOL() is not used, but #include <linux/export.h> is present

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20250612084257.200907-1-tzimmermann@suse.de

Author: tdz

drivers/gpu/drm/ast/ast_mode.c

@@ -29,7 +29,6 @@
  */
 
 #include <linux/delay.h>
-#include <linux/export.h>
 #include <linux/pci.h>
 
 #include <drm/drm_atomic.h>