rust: uaccess: name the correct function

Correctly refer to `reserve` rather than `try_reserve` in a comment. This
comment has been incorrect since inception in commit 1b580e7b9ba2 ("rust:
uaccess: add userspace pointers").

Fixes: 1b580e7b9ba2 ("rust: uaccess: add userspace pointers")
Signed-off-by: Tamir Duberstein <[e-mail]>
Reviewed-by: Alice Ryhl <[e-mail]>
Reviewed-by: Benno Lossin <[e-mail]>
Reviewed-by: Charalampos Mitrodimas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Miguel Ojeda <[e-mail]>

rust/kernel/uaccess.rs

···
         let len = self.length;
         buf.reserve(len, flags)?;
 
-        // The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
-        // long.
+        // The call to `reserve` was successful, so the spare capacity is at least `len` bytes long.
         self.read_raw(&mut buf.spare_capacity_mut()[..len])?;
 
         // SAFETY: Since the call to `read_raw` was successful, so the next `len` bytes of the