rust: firmware: 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>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://patch.msgid.link/20251113-core-cstr-cstrings-v3-1-411b34002774@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: tamird

rust/kernel/firmware.rs

@@ -51,13 +51,13 @@ impl FwFunc {
 /// # Examples
 ///
 /// ```no_run
-/// # use kernel::{c_str, device::Device, firmware::Firmware};
+/// # use kernel::{device::Device, firmware::Firmware};
 ///
 /// # fn no_run() -> Result<(), Error> {
 /// # // SAFETY: *NOT* safe, just for the example to get an `ARef<Device>` instance
 /// # let dev = unsafe { Device::get_device(core::ptr::null_mut()) };
 ///
-/// let fw = Firmware::request(c_str!("path/to/firmware.bin"), &dev)?;
+/// let fw = Firmware::request(c"path/to/firmware.bin", &dev)?;
 /// let blob = fw.data();
 ///
 /// # Ok(())
@@ -204,7 +204,7 @@ macro_rules! module_firmware {
     ($($builder:tt)*) => {
         const _: () = {
             const __MODULE_FIRMWARE_PREFIX: &'static $crate::str::CStr = if cfg!(MODULE) {
-                $crate::c_str!("")
+                c""
             } else {
                 <LocalModule as $crate::ModuleMetadata>::NAME
             };