rust: io: fix broken intra-doc links to platform::Device

`platform` is not accessible from here.

Thus fix the intra-doc links by qualifying the paths a bit more.

Fixes: 1d0d4b2 ("rust: io: mem: add a generic iomem abstraction")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20250722085500.1360401-2-ojeda@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: ojeda

rust/kernel/io/mem.rs

@@ -40,8 +40,8 @@ impl<'a> IoRequest<'a> {
     ///
     /// # Examples
     ///
-    /// The following example uses a [`platform::Device`] for illustration
-    /// purposes.
+    /// The following example uses a [`kernel::platform::Device`] for
+    /// illustration purposes.
     ///
     /// ```no_run
     /// use kernel::{bindings, c_str, platform, of, device::Core};
@@ -98,8 +98,8 @@ impl<'a> IoRequest<'a> {
     ///
     /// # Examples
     ///
-    /// The following example uses a [`platform::Device`] for illustration
-    /// purposes.
+    /// The following example uses a [`kernel::platform::Device`] for
+    /// illustration purposes.
     ///
     /// ```no_run
     /// use kernel::{bindings, c_str, platform, of, device::Core};