drm/nouveau/kms/nv50-: s/armh/asyh/ in nv50_msto_atomic_enable()

I have a strange dejavu feeling that I tried to submit a patch for this in
the past, but that it was rejected. I can't remember though, but I'm
further convinced this patch is the right thing to do anyway.

We label the to-be-committed head state in nv50_msto_atomic_enable() as
armh. Normally armh implies a state which is currently armed in hardware.
nv50_msto_atomic_enable() is called _after_ drm_atomic_swap_state()
however, but before the commit tail ends, which means that said state is
not actually armed on hardware.

As well - take note that this is the same convention followed in all of the
other atomic_enable() callbacks.

So, let's correct this to asyh.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>