mkfifo: fix build where mode_t is not u32

`rustix::fs::Mode` is a bitflags over `rustix::fs::RawMode`, which
aliases `libc::mode_t`. That is `u32` on Linux but `u16` on the BSDs,
so handing the `u32` mode straight to `Mode::from_bits_truncate()`
fails to compile there:

    error[E0308]: mismatched types
       --> src/uu/mkfifo/src/mkfifo.rs:146:50
        |
    146 |     mkfifoat(CWD, path, Mode::from_bits_truncate(mode))
        |                         ------------------------ ^^^^ expected `u16`, found `u32`

Cast to `RawMode` first, which is a no-op on Linux and matches what
`mkdir` already does in src/uu/mkdir/src/mkdir.rs.

Co-authored-by: oech3 <79379754+oech3@users.noreply.github.com>

Author: pkubaj

src/uu/mkfifo/src/mkfifo.rs

@@ -142,8 +142,12 @@ pub fn uu_app() -> Command {
 // the umask so the requested mode is applied atomically (see issue #10020).
 #[cfg(not(target_vendor = "apple"))]
 fn create_fifo(path: &str, mode: u32) -> Result<(), std::io::Error> {
-    use rustix::fs::{CWD, mkfifoat};
-    mkfifoat(CWD, path, Mode::from_bits_truncate(mode)).map_err(std::io::Error::from)
+    use rustix::fs;
+    Ok(fs::mkfifoat(
+        fs::CWD,
+        path,
+        Mode::from_bits_truncate(mode as fs::RawMode),
+    )?)
 }
 
 #[cfg(target_vendor = "apple")]