rust: time: add Delta::as_jiffies_unsigned()

Delta<Jiffy> is signed, but some C functions, such as
queue_delayed_work_on(), take a span in jiffies as unsigned long. So
each caller has to clamp a negative value to zero and cast it before
it passes the value to C. Add a helper that does both.

Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Acked-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20261002050428.2746277-3-tomo@flapping.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/time.rs

@@ -363,6 +363,27 @@ pub const fn from_jiffies(jiffies: isize) -> Self {
     pub const fn as_jiffies(self) -> isize {
         self.value
     }
+
+    /// Return the number of jiffies in the [`Delta`] as an unsigned value.
+    ///
+    /// If the number of jiffies is negative, zero is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use kernel::time::Delta;
+    ///
+    /// // A negative span returns zero.
+    /// assert_eq!(Delta::from_jiffies(-1).as_jiffies_unsigned(), 0);
+    ///
+    /// // A positive span returns its value.
+    /// assert_eq!(Delta::from_jiffies(1).as_jiffies_unsigned(), 1);
+    /// ```
+    #[inline]
+    pub fn as_jiffies_unsigned(self) -> usize {
+        // CAST: `isize::max()` makes the value non-negative, so the cast keeps it.
+        isize::max(self.value, 0) as usize
+    }
 }
 
 impl ops::Add for Delta {