drm/amdgpu: Fix potential NULL dereference

Fix potential NULL dereference, in the case when "man", the resource manager
might be NULL, when/if we print debug information.

Cc: Alex Deucher <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: AMD Graphics <[e-mail]>
Cc: Dan Carpenter <[e-mail]>
Cc: kernel test robot <[e-mail]>
Fixes: 7554886daa31ea ("drm/amdgpu: Fix size validation for non-exclusive domains (v4)")
Signed-off-by: Luben Tuikov <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_object.c

···
 	return true;
 
 fail:
-	DRM_DEBUG("BO size %lu > total memory in domain: %llu\n", size,
-		  man->size);
+	if (man)
+		DRM_DEBUG("BO size %lu > total memory in domain: %llu\n", size,
+			  man->size);
 	return false;
 }