Use C string literals not cstr!

Since Rust 1.77.0 the language has supported C string literals, so the
`cstr!` macro is no longer needed. Replace existing usages with the
equivalent literal.

See https://doc.rust-lang.org/reference/tokens.html#c-string-literals.

I believe that the two are equivalent:
- Escapes are handled the same way;
- Both allow arbitrary Unicode, which is mapped to UTF-8 (I don't
  think we made any use of this);
- Both treat any embedded NUL character as a compile time error.

This is of no significance whatsoever, but it does make the code a
tiny bit simpler. It should not change the compiled code at all, so
no flagging should be needed.

I'm not deleting the macro in this CL; I'll do a follow-up for that,
since there may be usages I can't see, and it has greater chance of
accidental conflict.

Test: TH
Change-Id: I4354b3b0a0c53fbec0c2d78b4182786e4e2d0ce8
diff --git a/libs/libvmbase/src/fdt.rs b/libs/libvmbase/src/fdt.rs
index aaf354e..2113787 100644
--- a/libs/libvmbase/src/fdt.rs
+++ b/libs/libvmbase/src/fdt.rs
@@ -17,7 +17,6 @@
 pub mod pci;
 
 use core::ops::Range;
-use cstr::cstr;
 use libfdt::{self, Fdt, FdtError};
 
 /// Represents information about a SWIOTLB buffer.
@@ -34,7 +33,7 @@
 impl SwiotlbInfo {
     /// Creates a `SwiotlbInfo` struct from the given device tree.
     pub fn new_from_fdt(fdt: &Fdt) -> libfdt::Result<Option<SwiotlbInfo>> {
-        let Some(node) = fdt.compatible_nodes(cstr!("restricted-dma-pool"))?.next() else {
+        let Some(node) = fdt.compatible_nodes(c"restricted-dma-pool")?.next() else {
             return Ok(None);
         };
         let (addr, size, align) = if let Some(mut reg) = node.reg()? {
@@ -42,8 +41,8 @@
             let size = reg.size.ok_or(FdtError::BadValue)?;
             (Some(reg.addr.try_into().unwrap()), size.try_into().unwrap(), None)
         } else {
-            let size = node.getprop_u64(cstr!("size"))?.ok_or(FdtError::NotFound)?;
-            let align = node.getprop_u64(cstr!("alignment"))?.ok_or(FdtError::NotFound)?;
+            let size = node.getprop_u64(c"size")?.ok_or(FdtError::NotFound)?;
+            let align = node.getprop_u64(c"alignment")?.ok_or(FdtError::NotFound)?;
             (None, size.try_into().unwrap(), Some(align.try_into().unwrap()))
         };
         Ok(Some(Self { addr, size, align }))