nir: Reassociate N-R for frsq.

Makes things even worse:

total instructions in shared programs: 91073 -> 91407 (0.37%)
instructions in affected programs:     35494 -> 35828 (0.94%)
total uniforms in shared programs: 33351 -> 33243 (-0.32%)
uniforms in affected programs:     2953 -> 2845 (-3.66%)
total estimated cycles in shared programs: 254359 -> 254733 (0.15%)
estimated cycles in affected programs:     92912 -> 93286 (0.40%)