[mlir] Fix exiting OpPatternRewriteDriver::simplifyLocally after first...

[mlir] Fix exiting OpPatternRewriteDriver::simplifyLocally after first iteration that didn't change the op.

Before this change, we would run `maxIterations` if the first iteration changed the op.
After this change, we exit the loop as soon as an iteration hasn't changed the op.
Assuming that we have reached a fixed point when an iteration doesn't change the op, this doesn't affect correctness.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D89981