rust: sync: add missing newline in locked_by log example

rust: sync: add missing newline in locked_by log example

The pr_info! example in rust/kernel/sync/locked_by.rs was missing
a newline. This patch appends the missing newline to ensure
that log messages for locked resources display correctly.

Fixes: 7b1f55e3a984 ("rust: sync: introduce `LockedBy`")
Reported-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1139
Signed-off-by: Alban Kurti <kurti@invicto.ai>
Link: https://lore.kernel.org/r/20250206-printing_fix-v3-4-a85273b501ae@invicto.ai
[ Replaced Closes with Link since it fixes part of the issue. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>