drm/panthor: Fix OPP refcnt leaks in devfreq initialisation

Rearrange lookup of recommended OPP for the Mali GPU device and its refcnt
decremental to make sure no OPP object leaks happen in the error path.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Fixes: fac9b22d ("drm/panthor: Add the devfreq logical block")
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241105205458.1318989-2-adrian.larumbe@collabora.com