pwm: th1520: 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.

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Michal Wilczynski <m.wilczynski@samsung.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://patch.msgid.link/20251222-cstr-pwm-v1-1-e8916d976f8d@gmail.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: tamird

drivers/pwm/pwm_th1520.rs

@@ -22,7 +22,6 @@
 
 use core::ops::Deref;
 use kernel::{
-    c_str,
     clk::Clk,
     device::{Bound, Core, Device},
     devres,
@@ -327,7 +326,7 @@ kernel::of_device_table!(
     OF_TABLE,
     MODULE_OF_TABLE,
     <Th1520PwmPlatformDriver as platform::Driver>::IdInfo,
-    [(of::DeviceId::new(c_str!("thead,th1520-pwm")), ())]
+    [(of::DeviceId::new(c"thead,th1520-pwm"), ())]
 );
 
 impl platform::Driver for Th1520PwmPlatformDriver {