ir3/cp_postsched: Fixup SSA use pointer for direct reads

ir3/cp_postsched: Fixup SSA use pointer for direct reads

There's an optimization here to sink direct (i.e. not relative) reads of
an array past unrelated direct writes. However, since each write
actually reads, modifies, and then writes again to the array, this means
that we need to read the latest updated array. The old RA used the array
id instead of the SSA information, so it didn't care, but the new RA
uses ->instr instead and ignores the array id because arrays are now SSA
so it needs to be correct.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10591>