freedreno/ir3: clean up dangling false-dep's

freedreno/ir3: clean up dangling false-dep's

Maybe there is a better way for this..  where it comes useful is "array"
loads, which end up as a false-dep for a later array store.

If all the uses of an array load are CP'd into their consumer, it still
leaves the dangling array load, leading to funny things like:

  mov.u32u32 r5.y, r0.y
  mov.u32u32 r5.y, r0.z

Signed-off-by: Rob Clark <robdclark@gmail.com>