drm/sched: Qualify drm_sched_wakeup() by drm_sched_entity_is_ready()

Don't "wake up" the GPU scheduler unless the entity is ready, as well as we
can queue to the scheduler, i.e. there is no point in waking up the scheduler
for the entity unless the entity is ready.

Signed-off-by: Luben Tuikov <ltuikov89@gmail.com>
Fixes: bc8d6a9d

 ("drm/sched: Don't disturb the entity when in RR-mode scheduling")
Reviewed-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231110000123.72565-2-ltuikov89@gmail.com