[mlir][mesh] Exit after signalPassFailure to fix a crash (#132662)

Fixes #131435.

mlir/lib/Dialect/Mesh/Transforms/ShardingPropagation.cpp

@@ -369,7 +369,7 @@ struct ShardingPropagation
     OpBuilder builder(ctx);
     if (!region.hasOneBlock()) {
       funcOp.emitOpError() << "only one block is supported!";
-      signalPassFailure();
+      return signalPassFailure();
     }
     Block &block = region.front();
 

mlir/test/Dialect/Mesh/sharding-propagation-failed.mlir

@@ -0,0 +1,4 @@
+// RUN: mlir-opt --pass-pipeline="builtin.module(func.func(sharding-propagation))" %s -verify-diagnostics
+
+// expected-error @+1 {{'func.func' op only one block is supported!}}
+func.func private @no_block_function(i64)