drm/amd/display: remove oem i2c adapter on finish

Fixes a bug where unbinding of the GPU would leave the oem i2c adapter
registered resulting in a null pointer dereference when applications try
to access the invalid device.

Fixes: 3d5470c ("drm/amd/display/dm: add support for OEM i2c bus")
Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Geoffrey McRae <geoffrey.mcrae@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 89923fb)
Cc: stable@vger.kernel.org

Author: gnifAMD

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -2913,6 +2913,17 @@ static int dm_oem_i2c_hw_init(struct amdgpu_device *adev)
 	return 0;
 }
 
+static void dm_oem_i2c_hw_fini(struct amdgpu_device *adev)
+{
+	struct amdgpu_display_manager *dm = &adev->dm;
+
+	if (dm->oem_i2c) {
+		i2c_del_adapter(&dm->oem_i2c->base);
+		kfree(dm->oem_i2c);
+		dm->oem_i2c = NULL;
+	}
+}
+
 /**
  * dm_hw_init() - Initialize DC device
  * @ip_block: Pointer to the amdgpu_ip_block for this hw instance.
@@ -2963,7 +2974,7 @@ static int dm_hw_fini(struct amdgpu_ip_block *ip_block)
 {
 	struct amdgpu_device *adev = ip_block->adev;
 
-	kfree(adev->dm.oem_i2c);
+	dm_oem_i2c_hw_fini(adev);
 
 	amdgpu_dm_hpd_fini(adev);