[MLIR] Add memref dialect dependency for affine fusion pass

For `AffineLoopFusion` pass, add `memref` dialect as a dependent
dialect. Since the fusion pass can create `memref::AllocOp`s, the
dialect must be registered in its dependent dialects.

The missing dependency was not discovered until now because the above
said op creation happes only when the input already has
`memref::AllocOp`s in it, and all dialects in the input are
automatically added to the context.

Reviewed By: bondhugula

Differential Revision: https://reviews.llvm.org/D102104