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 1b580e7b ("rust:
uaccess: add userspace pointers").

Fixes: 1b580e7b ("rust: uaccess: add userspace pointers")
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Charalampos Mitrodimas <charmitro@posteo.net>
Link: https://lore.kernel.org/r/20250317-uaccess-typo-reserve-v1-1-bbfcb45121f3@gmail.com


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>