The assignment of err is using the incorrect pointer vaddr that has
not been initialized. Fix this by using the correct pointer obj instead.

Addresses-Coverity: ("Uninitialized pointer read")
Fixes: 6501aa4e ("drm/i915: add in-kernel blitter client")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190531103201.10124-1-colin.king@canonical.com