[mlir] Fixed alignment attribute of alloc constant folding.

When allocLikeOp is updated in alloc constant folding,
alighnment attribute was ignored. This patch fixes it.

Signed-off-by: Haruki Imai <imaihal@jp.ibm.com>

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D99882