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/guest/vmbase_example/src/main.rs b/guest/vmbase_example/src/main.rs
index 4c5e880..f5b41bd 100644
--- a/guest/vmbase_example/src/main.rs
+++ b/guest/vmbase_example/src/main.rs
@@ -27,7 +27,6 @@
 use crate::pci::check_pci;
 use alloc::{vec, vec::Vec};
 use core::ptr::addr_of_mut;
-use cstr::cstr;
 use libfdt::Fdt;
 use log::{debug, error, info, trace, warn, LevelFilter};
 use vmbase::{
@@ -147,7 +146,7 @@
         info!("memory @ {reg:#x?}");
     }
 
-    let compatible = cstr!("ns16550a");
+    let compatible = c"ns16550a";
 
     for c in reader.compatible_nodes(compatible).unwrap() {
         let reg = c.reg().unwrap().unwrap().next().unwrap();
@@ -159,17 +158,17 @@
     writer.unpack().unwrap();
     info!("FDT successfully unpacked.");
 
-    let path = cstr!("/memory");
+    let path = c"/memory";
     let node = writer.node_mut(path).unwrap().unwrap();
-    let name = cstr!("child");
+    let name = c"child";
     let mut child = node.add_subnode(name).unwrap();
     info!("Created subnode '{}/{}'.", path.to_str().unwrap(), name.to_str().unwrap());
 
-    let name = cstr!("str-property");
+    let name = c"str-property";
     child.appendprop(name, b"property-value\0").unwrap();
     info!("Appended property '{}'.", name.to_str().unwrap());
 
-    let name = cstr!("pair-property");
+    let name = c"pair-property";
     let addr = 0x0123_4567u64;
     let size = 0x89ab_cdefu64;
     child.appendprop_addrrange(name, addr, size).unwrap();