rust: init: update stack_try_pin_init examples

Change documentation imports to use `kernel::alloc::AllocError`,
because `KBox::new()` now returns that, instead of the `core`'s
`AllocError`.

Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Jimmy Ostler <jtostler1@gmail.com>
Link: https://lore.kernel.org/r/ec8badbe94c5e78f22315325a7f2ae96129d6a65.1734674670.git.jtostler1@gmail.com
[ Fixed formatting of imports (still unordered). Slightly reworded
  commit. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: LordGoatius

rust/kernel/init.rs

@@ -290,9 +290,17 @@ macro_rules! stack_pin_init {
 ///
 /// ```rust,ignore
 /// # #![expect(clippy::disallowed_names)]
-/// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
+/// # use kernel::{
+/// #     init,
+/// #     pin_init,
+/// #     stack_try_pin_init,
+/// #     init::*,
+/// #     sync::Mutex,
+/// #     new_mutex,
+/// #     alloc::AllocError,
+/// # };
 /// # use macros::pin_data;
-/// # use core::{alloc::AllocError, pin::Pin};
+/// # use core::pin::Pin;
 /// #[pin_data]
 /// struct Foo {
 ///     #[pin]
@@ -316,9 +324,17 @@ macro_rules! stack_pin_init {
 ///
 /// ```rust,ignore
 /// # #![expect(clippy::disallowed_names)]
-/// # use kernel::{init, pin_init, stack_try_pin_init, init::*, sync::Mutex, new_mutex};
+/// # use kernel::{
+/// #     init,
+/// #     pin_init,
+/// #     stack_try_pin_init,
+/// #     init::*,
+/// #     sync::Mutex,
+/// #     new_mutex,
+/// #     alloc::AllocError,
+/// # };
 /// # use macros::pin_data;
-/// # use core::{alloc::AllocError, pin::Pin};
+/// # use core::pin::Pin;
 /// #[pin_data]
 /// struct Foo {
 ///     #[pin]