drm/sched: Stop setting current entity in FIFO mode

It does not seem there is a need to set the current entity in FIFO mode
since ot only serves as being a "cursor" in round-robin mode. Even if
scheduling mode is changed at runtime the change in behaviour is simply
to restart from the first entity, instead of continuing in RR mode from
where FIFO left it, and that sounds completely fine.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Luben Tuikov <ltuikov89@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <pstanner@redhat.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241016122013.7857-3-tursulin@igalia.com