rust: uaccess: generalize write_dma() to accept any Coherent<T>

rust: uaccess: generalize write_dma() to accept any Coherent<T>

Generalize write_dma() from &Coherent<[u8]> to &Coherent<T> where
T: KnownSize + AsBytes + ?Sized. The function body only uses as_ptr()
and size(), which work for any such T, so there is no reason to
restrict it to byte slices.

Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260325003921.3420-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>