agp: Include "compat_ioctl.h" where necessary

Fix compiler warnings like

  drivers/char/agp/frontend.c:46:20: warning: no previous prototype for 'agp_find_mem_by_key' [-Wmissing-prototypes]
    46 | struct agp_memory *agp_find_mem_by_key(int key)

by including the compat_ioctl.h in the source file.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20211201114645.15384-3-tzimmermann@suse.de

drivers/char/agp/frontend.c

@@ -39,7 +39,9 @@
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
+
 #include "agp.h"
+#include "compat_ioctl.h"
 
 struct agp_front_data agp_fe;