drm/gud: Fix UBSAN warning

UBSAN complains about invalid value for bool:

[  101.165172] [drm] Initialized gud 1.0.0 20200422 for 2-3.2:1.0 on minor 1
[  101.213360] gud 2-3.2:1.0: [drm] fb1: guddrmfb frame buffer device
[  101.213426] usbcore: registered new interface driver gud
[  101.989431] ================================================================================
[  101.989441] UBSAN: invalid-load in linux/include/linux/iosys-map.h:253:9
[  101.989447] load of value 121 is not a valid value for type '_Bool'
[  101.989451] CPU: 1 PID: 455 Comm: kworker/1:6 Not tainted 5.18.0-rc5-gud-5.18-rc5 #3
[  101.989456] Hardware name: Hewlett-Packard HP EliteBook 820 G1/1991, BIOS L71 Ver. 01.44 04/12/2018
[  101.989459] Workqueue: events_long gud_flush_work [gud]
[  101.989471] Call Trace:
[  101.989474]  <TASK>
[  101.989479]  dump_stack_lvl+0x49/0x5f
[  101.989488]  dump_stack+0x10/0x12
[  101.989493]  ubsan_epilogue+0x9/0x3b
[  101.989498]  __ubsan_handle_load_invalid_value.cold+0x44/0x49
[  101.989504]  dma_buf_vmap.cold+0x38/0x3d
[  101.989511]  ? find_busiest_group+0x48/0x300
[  101.989520]  drm_gem_shmem_vmap+0x76/0x1b0 [drm_shmem_helper]
[  101.989528]  drm_gem_shmem_object_vmap+0x9/0xb [drm_shmem_helper]
[  101.989535]  drm_gem_vmap+0x26/0x60 [drm]
[  101.989594]  drm_gem_fb_vmap+0x47/0x150 [drm_kms_helper]
[  101.989630]  gud_prep_flush+0xc1/0x710 [gud]
[  101.989639]  ? _raw_spin_lock+0x17/0x40
[  101.989648]  gud_flush_work+0x1e0/0x430 [gud]
[  101.989653]  ? __switch_to+0x11d/0x470
[  101.989664]  process_one_work+0x21f/0x3f0
[  101.989673]  worker_thread+0x200/0x3e0
[  101.989679]  ? rescuer_thread+0x390/0x390
[  101.989684]  kthread+0xfd/0x130
[  101.989690]  ? kthread_complete_and_exit+0x20/0x20
[  101.989696]  ret_from_fork+0x22/0x30
[  101.989706]  </TASK>
[  101.989708] ================================================================================

The source of this warning is in iosys_map_clear() called from
dma_buf_vmap(). It conditionally sets values based on map->is_iomem. The
iosys_map variables are allocated uninitialized on the stack leading to
->is_iomem having all kinds of values and not only 0/1.

Fix this by zeroing the iosys_map variables.

Fixes: 40e1a70b ("drm: Add GUD USB Display driver")
Cc: <stable@vger.kernel.org> # v5.18+
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221122-gud-shadow-plane-v2-1-435037990a83@tronnes.org

drivers/gpu/drm/gud/gud_pipe.c

@@ -157,8 +157,8 @@ static int gud_prep_flush(struct gud_device *gdrm, struct drm_framebuffer *fb,
 {
 	struct dma_buf_attachment *import_attach = fb->obj[0]->import_attach;
 	u8 compression = gdrm->compression;
-	struct iosys_map map[DRM_FORMAT_MAX_PLANES];
-	struct iosys_map map_data[DRM_FORMAT_MAX_PLANES];
+	struct iosys_map map[DRM_FORMAT_MAX_PLANES] = { };
+	struct iosys_map map_data[DRM_FORMAT_MAX_PLANES] = { };
 	struct iosys_map dst;
 	void *vaddr, *buf;
 	size_t pitch, len;