floppy: cleanup: make output_byte() not rely on current_fdc anymore

Now the fdc is passed in argument so that the function does not
use current_fdc anymore.

Link: https://lore.kernel.org/r/20200331094054.24441-14-w@1wt.eu


Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Denis Efremov <efremov@linux.com>