Pin vm-memory to 0.17.1

As reported in https://github.com/rust-vmm/vm-memory/pull/369,
vm-memory 0.17.2:
    breaks the vhost-user-backend crate, whose vring types require some
    type `M: GuestAddressSpace` with the expectation that `M::memory()`
    will return something that derefs to an `0.17::GuestMemory`"

So let's pin vm-memory to 0.17.1 for now while waiting for 0.17.3 release
that will include that fix.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Cargo.toml

@@ -9,5 +9,5 @@ members = [
 [workspace.dependencies]
 virtio-bindings = "0.2.6"
 virtio-queue = "0.17.0"
-vm-memory = "0.17.1"
+vm-memory = "=0.17.1"
 vmm-sys-util = "0.15.0"