[mlir][linalg] fix specialization of transposed matmul variants (#181387)
Currently all generics that represent `linalg.matmul_transpose_a/b`
variants will get specialized to a regular `linalg.matmul` without any
special indexing maps. This patch fixes this behavior to correctly emit
`linalg.matmul` with the correct indexing maps for the transposed
variants.