block/floppy: Convert callback to pass timer_list

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to passing in the timer pointer explicitly.
Calculate the drive from the offset of the timer in the timer list.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Geliang Tang <geliangtang@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>