gpu: host1x: do not check previously handled gathers

When patching gathers, we don't need to check against
gathers with lower indices than the current one, as
they are guaranteed to already have been handled.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Acked-By: Terje Bergstrom <tbergstrom@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>