kgdb: rectify kernel-doc for kgdb_unregister_io_module()

The command 'find ./kernel/debug/ | xargs ./scripts/kernel-doc -none'
reported a typo in the kernel-doc of kgdb_unregister_io_module().

Rectify the kernel-doc, such that no issues remain for ./kernel/debug/.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20210125144847.21896-1-lukas.bulwahn@gmail.com


Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>