This fix was written against drm-next, but when it was
backported to 4.5 as a stable fix, the driver internal
structure change was missed.  Fix that up here to avoid
a hang due to waiting for the wrong sequence number.

v2: agd: fix up commit message
Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>