drm/ttm: fix condition (and vs or)

The "if (!p && !p->dev)" condition isn't right because || was intended
instead of &&.  But actually, "p" is the list cursor and so it's always
non-NULL and we can just remove that bit.  We can remove the another
similar check as well.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>