gpu: nova: replace `kernel::c_str!` with C-Strings

gpu: nova: replace `kernel::c_str!` with C-Strings

C-String literals were added in Rust 1.77. Replace instances of
`kernel::c_str!` with C-String literals where possible.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://patch.msgid.link/20251222-cstr-nova-v1-1-0e2353d5debe@gmail.com
[ Use 'nova' commit subject prefix; use kernel vertical import style.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>