drm/nv50-nv84/fifo: fix resume regression introduced by playlist race fix

Reported-by: Maarten Maathuis <madman2003@gmail.com>
Reported-by: Sven Joachim <svenjoac@gmx.de>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>