rust: error: Add EOVERFLOW

rust: error: Add EOVERFLOW

Trivial addition for missing EOVERFLOW error. This is used by a
subsequent patch that might require returning EOVERFLOW as a result
of `checked_mul`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250317185345.2608976-2-abdiel.janulgue@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>