[inductor] Fix broadcast of random seed in mm epilogue (#97591)
Fixes #96468, #97553
In matmul codegen epilogue we use `mask` shape to infer the broadcasted shape in case we need to broadcast a scalar value.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97591
Approved by: https://github.com/jansel
Author
Natalia Gimelshein
