Revert "coredump: Remove the WARN_ON in dump_vma_snapshot"

This reverts commit b043ae63.

It breaks the abi and is not needed for Android devices so it can be
dropped.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I565f6e1c6053b1d43aa7fb69e0f6b533401d16be