Loop coalescing: fix pointer chainsing in use-chain traversal

In the replaceAllUsesExcept utility function called from loop coalescing the
iteration over the use-chain is incorrect. The use list nodes (IROperands) have
next/prev links, and bluntly resetting the use would make the loop to continue
on uses of the value that was replaced instead of the original one. As a
result, it could miss the existing uses and update the wrong ones. Make sure we
increment the iterator before updating the use in the loop body.

Reported-by: Uday Bondhugula <uday@polymagelabs.com>

Closes tensorflow/mlir#291.

PiperOrigin-RevId: 283754195