Set `BLAS_LIBRARIES` to `${MKL_LIBRARIES}` for MKL case (#72806)
This reverts [suggestion](https://github.com/pytorch/pytorch/pull/49647#discussion_r677737470) proposed to https://github.com/pytorch/pytorch/pull/49647
Which is somehow sufficient to workaround symptoms of https://github.com/pytorch/pytorch/issue/72653
I.e. before this change, `BLAS_LIBRARIES` were set to `caffe2::mkl`
which is an interface library with link property set as follows:
https://github.com/pytorch/pytorch/blob/59dd84cab6ede977173cd48d64abf1bcf6b2fabb/cmake/public/mkl.cmake#L10-L12
