[mlir][docs] Fix incorrect operation name(NFC) (#109261)

Author: csstormq

mlir/docs/Dialects/Affine.md

@@ -372,7 +372,7 @@ Syntax:
 operation ::= `affine.dma_wait` ssa-use `[` multi-dim-affine-map-of-ssa-ids `]`, ssa-use `:` memref-type
 ```
 
-The `affine.dma_start` op blocks until the completion of a DMA operation
+The `affine.dma_wait` op blocks until the completion of a DMA operation
 associated with the tag element `%tag[%index]`. `%tag` is a memref, and `%index` has
 to be an index with the same restrictions as any load/store index. In
 particular, index for each memref dimension must be an affine expression of loop