drm/etnaviv: avoid cleaning up sched_job when submit succeeded

While the labels may mislead the casual reader, the tail of the function
etnaviv_ioctl_gem_submit is always executed, as a lot of the structures
set up in this function need to be cleaned up regardless of whether the
submit succeeded or failed.

An exception is the newly added drm_sched_job_cleanup, which must only
be called when the submit failed before handing the job to the
scheduler.

Fixes: b827c84f ("drm/etnaviv: Use scheduler dependency handling")
Reported-by: Michael Walle <michael@walle.cc>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504090229.2506560-1-l.stach@pengutronix.de