drm/omapdrm: Annotate dma-fence critical section in commit path

Nothing special, just put the end right after hw_done(). Note that in
one path there's a wait for the flip/update to complete. But as far as
I understand from comments and code that's only relevant for modesets,
and skipped if there wasn't a modeset done on a given crtc.

For a bit more clarity pull the hw_done() call out of the if/else,
that way it's a bit clearer flow. But happy to shuffle this around as
is seen fit.

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121152959.1725404-9-daniel.vetter@ffwll.ch