rust: scatterlist: import ResourceSize from kernel::io

rust: scatterlist: import ResourceSize from kernel::io

Now that ResourceSize has been moved to kernel::io, import it from the
io module instead of the io::resource sub-module. It makes sense in this
case since the dma_len isn't really related to the Resource type even
though both are sizes of allocations in physical ram.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251112-resource-phys-typedefs-v2-3-538307384f82@google.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>