lib/commonio.[ch]: struct commonio_ops: Add prefix 'cio_' to structure members

lib/commonio.[ch]: struct commonio_ops: Add prefix 'cio_' to structure members

This structure has members that are named like libc APIs.

libc is allowed to provide any functions as macros (7.1.4p1 in C23).

This means that libc is allowed to provide a free(3) macro, which could
look like

	#define free(p)  __free(p)

And that would be expanded by the preprocessor in our code, turning our
structure members into some code that won't work (or even worse, it
might misbehave).

So, fix this undefined behavior.

Signed-off-by: Alejandro Colomar <alx@kernel.org>