drm/ttm/tests: Set DMA mask in KUnit device

In commit d393acce ("drm/tests: Switch to kunit devices"),
DRM test helpers migrated away from using a dummy platform driver
in favour of KUnit device. This means that DMA masks for the device
are not set but are required by ttm_pool_alloc tests.

Set the DMA mask for coherent mappings to unblock testing.
Signed-off-by: Karolina Stolarek <karolina.stolarek@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/dbd83b01bc835d922c070ad1c5bd9023e631e6c4.1718192625.git.karolina.stolarek@intel.com

drivers/gpu/drm/ttm/tests/ttm_kunit_helpers.c

@@ -103,6 +103,9 @@ struct ttm_test_devices *ttm_test_devices_basic(struct kunit *test)
 	devs->dev = drm_kunit_helper_alloc_device(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, devs->dev);
 
+	/* Set mask for alloc_coherent mappings to enable ttm_pool_alloc testing */
+	devs->dev->coherent_dma_mask = -1;
+
 	devs->drm = __drm_kunit_helper_alloc_drm_device(test, devs->dev,
 							sizeof(*devs->drm), 0,
 							DRIVER_GEM);