drm/nouveau: fix pm initialization order

If nouveau_pm_perflvl_get() fails, pm->profiles list will be left
uninitialized, which causes oops during nouveau_pm_fini().

Move INIT_LIST_HEAD before call to nouveau_pm_perflvl_get().

Signed-off-by: Dmitry Eremin-Solenikov <dmitry_eremin@mentor.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>